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Full text of "Practical chemistry"




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PRACTICAL CHEMISTRY 



BY 
LYMAN C. NEWELL, Ph.D. (johns hopkins) 

PROFESSOR OF CHEMISTRY, BOSTON UJaVERSITV, BOSTON, MASS. 

AUTHOR OF 

"EXPERIMENTAL CHEXHSTRY,"' "DESCRIPTIVE CHEMISTRY" 

" GENERAL CHEMISTRY," " INORGANIC CHEMISTRY FOR 

COLLEGES," "LABORATORY MANUAL OF 

INORGANIC CHEMISTRY" 



D. C. HEATH & CO., PUBLLSHERS 

BOSTON Xt.W YORK CHICAGO 



Q 



COPYRIGHT, 1922 
BY LYMAN C. NEWELL 



2G 



^ ( 
33 



PREFACE 

A TEXTBOOK intended for the first year of chemistry should nu-it 
certain requirements. Both pupil and teacher must be considin-d. 
The pupil needs a book which is written plainly, illustrated fully, 
and applied practically; which stimulates interest in chemistrv, and 
which can be studied profitably. The teacher needs a b;)ok in which 
the text is carefully selected, judiciously apportioned, and properlv 
arranged ; which provides teaching material, and which can be taught 
successfully. The author believes his Practical Chemistry meets 
these requirements. 

The text includes the facts and principles suitable for beirinncrs. 
No important topic has been omitted. The selection is varied. i)er- 
mitting the use of the book in different kinds of classes. The topics 
suggested by the College Entrance Examination Board and the 
Board of Regents (New York) have been incorporated. 

The style and arrangement are clear — short sentences, brief para- 
graphs, explanatory examples, lettered subdivisions, numbered sec- 
tions, instructive topical headings. Unusual care has been taken to 
write clearly such topics as symbols, formulas, equations, atomic 
weights, molecular weights, and valence. 

The exercises, which are placed at the end of the chapters, have l)ecn 
prepared to meet the real needs of pupils. The author believes that 
a class should be drilled on fundamentals as well as provided with 
opportunities to answer test questions. Hence, numerous exercises 
have been provided for review, home study, practical e.xpcrience. 
and themes. Teachers are urged to examine these exercises and as- 
sign those best adapted to the needs of the class. The list of books 
incorporated in the Appendix, § 5, will be serviceable in connection with 
home study and other assignments. 

The problems emphasize fundamental principles and processes; 
many require original thinking. The liberal selection will meet the 
requirements of different kinds of classes. 

An examination of the book will show that it is a Practical Chem- 
istry — practical in several ways. The more vital applications of 
chemistry are described in connection with the appropriate facts or 
principles. IMoreover, the major applications of chemistry are so 
fully described and illustrated that a pupil can obtain from the book 
itself an accurate and adequate account of modern chemical indus- 



iv PREFACE 

tries. Teachers are referred to such topics as purification of water 
(69), nitric acid (196), sulphur (250), sulphuric acid (268, 270), fuel 
oil and gasolene (311, 312. Fig. 112), sodium silicate (387), glass 
(394), cast iron (490), steel (494. 495) ^ and copper (528, Fig. 193). 
' Certain features of this book should not be overlooked. 

(i) The study of carbon is begun in Chapter III, thereby introduc- 
ing a famihar element and its striking applications at the start. This 
element is reviewed (with extensions) in Chapter XXI, and its useful 
compounds are studied in Chapters XXII (Fuels and Illuminants), 
XXIII (Other Carbon Compounds), and XXIV (Food). No apol- 
ogy is offered for devoting so much space to carbon. It is a funda- 
mental element, and the practical apphcations of this element and 
its compounds are indispensable and conspicuous. 

(2) The portion of the text that deals with theory is thoroughly 
adequate. The material is strategically distributed among several 
chapters (VII, VIII, X, XV, XVI, XVII). This distribution, as 
well as the simple treatment, will make the theory of chemistry less 
formidable to beginners. 

(3) Certain metals are treated rather fully and placed in the first 
part of the text devoted to metals. These are sodium, calcium, iron, 
aluminium, and copper (Chapters XXIX-XXXIII) . By this ar- 
rangement the essential principles of metallurgy, the characteristics 
of metals, and the apphcations of metals and their compounds are 
available for study before the hurried work at the close of the year. 

(4) Half-tone illustrations have been liberally used because they 
tell a story which is often more complete than verbal description. 
The author trusts they will be made indispenable adjuncts to instruc- 
tion. The portraits of chemists, which were made from originals in 
the author's private collection, have been inserted to arouse interest 
in those chemists who have contributed conspicuously to the founding 
and progress of chemistry. 

(5) The drawings of processes and apparatus are likewise intended 
as a supplement to the text. Especial care has been taken to draw 
them accurately and to represent salient features without confusing 
details. These drawings, with minor exceptions, were made by Har- 
old C. Spencer, Boston University, 1914- The author is deeply in- 
debted to him for commendable patience and skillful cooperation. 

The author is grateful for suggestions and assistance received from 
members of the faculty of Boston University and from former stu- 
dents who are teaching chemistry in high schools. 

L. C. N. 

Boston, Mass. 
May, 1922. 



ACKNO\M.EDGMEXTS 

The author acknowledges the courtesy and Kcnerosily of the fol- 
lowing for the use of photographs : -- 
Acheson Graphite Co., Niagara Falls, X. V. ( loo) ; 
Air Reduction Sales Co., N. Y. (28, 125) ; 

American Agricultural Chemical Co., Boston, Mass. (152, i53) ; 
American La France Fire Engine Company of Massachusetts, Boston, 

Mass. (18); 
Board of Water Supply — City of New York, X. \ . (34) ; 
Bureau of Mines, Washington, D. C. (iij ; 
Commonwealth Steel Co., St. Louis, Mo. (181); 
Coors Porcelain Co., Golden, Colo. (192) ; 

Electro Bleaching Gas Co., N. Y. (63) ; 

Freeport Sulphur Co., N. Y. (89) ; 

Honolulu Iron Works, N. Y. (132, i33. i34) ; 

Illinois Glass Co., and Editor of Bottles, Alton, 111. (146) ; 

Libbev-Owens Sheet Glass Co.. Charleston, W . \ a. (145) ; 

Lurav Caverns Corporation, Luray, Va. (162) ; 

Macbeth, Evans Co., Pittsburgh, Pa. (144) "' . ^ ^ , 

Ma-nesia Association of America, Philadelphia, Pa. (200, 201); 

Metal & Thermit Co., N. Y. (189 — left, 190) ; 

National Lime Association, Washington, D. C. (160) ; 

New England Oil Refining Co., Boston, Mass. (iii, 113); 

Niagara Alkali Co., Niagara Falls, N. Y. (157) ; , ^ . . . 

Oxygen Products Co. and Electrolabs Co., Pittsburgh, Pa. (4), 

Petroleum Age, Chicago, III. (no) ; 

Philadelphia Quartz Co., Philadelphia, Pa. (143); 

Raritan Copper Works, Perth Amboy, N. J. (194, i95, ^^^^ ^°^' °'\-°'^ 

Rhode Island Agricultural Experiment Station, Kingston, R. I. (lOi), 

Riter-Conley Co., Pittsburgh, Pa. (172) ; 

Semet-Solvay Co., Syracuse, N. Y. (104) ; 

Swift & Co., Chicago, 111. (138) ; 

Texas Gulf Sulphur Co., N. Y. (90) ; 

Thermal Syndicate, Ltd., N. Y. (142) ; - u* a\- 

Underwood & Underwood, N. Y. (183, 184, 185 copyrighted) . 

Vulcan Iron Works, Wilkes-Barre, Pa. (167) ; 

Wallace & Tiernan Co., Inc., Newark. N. J. ^3:^) . 

S. D. Warren Co., Boston, Mass. (136, i37) ; 

Welsbach Co., Gloucester, N. J. (131); 

AiIa Wood Iron & steel Co., Philadelphm I.-.. (..^V. 

Youngstown Sheet & Tube Co., YounRstown, Oh.o (■„, .,S. ,8.), 



CH.\PTER 
I. 



II. 
III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 

XIII. 

XIV. 

XV. 

XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

XXI. 

XXII. 
XXIII. 



CONTENTS 

Chemical Ch.\nge — Elements — Compoun'ds — 

Law of Constant Composition . . . . 

Oxygen 

Carbon and Its Oxides — Law of Multiple Pkd- 

portions 
Hydrogen .... 
Measurement of Gases . 
Water — Law of Gas X'olumes — Hydrogen 

Peroxide 

Atomic Theory — Atoms and Molecules 

Symbols axd Formulas .... 

Xitrogen — Air — Argon — Helium — Liquid Air 

Reactions and Equations 

Chlorint: — Hydrochloric Acid 

Acids — Bases — Salts — Neutralization 

Ammonia — Ammonium Compounds . 

Nitric Acid — Nitrogen Oxides . 

Molecular Weights and For.milas 

Atomic Weights 

Valence .... 

Ions and Ionization 

Sulphur — Sulphides 

Sulphur Oxides, Acids, and Salts 

Carbon — Carbonic Acid - Carbon atks 

Oxides — Carbides 

Fuels — Illuminants — Fla.mk 

Other Carbon Compounds . . . • 



^5 
50 

50 

^7 

lOJ 

1 1 > 

I :') 

I V) 

1 7 ' 
10: 






vu 



Vlll 



CONTENTS 



CHAPTER 

XXIV. 

XXV. 

XXVL 

XXMI. 
XXVIII. 

XXIX. 

XXX. 

XXXI. 

XXXII. 

XXXIII. 

XXXIV. 

XXXV. 

XXXVI. 

XXXVII. 

XXXVIII. 



Food 

Silica — Silicates — Glass 

Metals and Non-Metals — Periodic Classi- 
fication ....... 

Fluorine — Bromine — Iodine . 

Phosphorus — Phosphates — Arsenic — Anti 
MONY — Bismuth . . . 

Sodium — Potassium ...... 

Calcium Carbonate — Lime — Cement . 

Iron and Steel 

Aluminium — Clay — Porcelain 

Copper 

Magnesium — Zinc — INIercury 

Tin — Lead 

SiL\'ER — Photography — Gold 

Chromium — IVIanganese — Platinum - 
Nickel — Cobalt 

Radium and Radioactivity 

Appendix 

Metric System 

Thermometers 

Weights of Gases 

\"apor Pressure 

Books . . . • • • • 



Index 



PAGE 
316 

337 

346 
360 
376 
391 
415 
426 

439 
452 
464 

474 
482 



493 
493 
493 
494 
494 
497 



PRACTICAL CHEMISTRY 



CHAPTER I 



CHEMICAL CHANGE — COMPOUNDS — ELEMENTS 



1. What is chemistry? — If we light a candle and let 
it burn, the candle wax slowly disappears — '' burns away.'' 
Let us study this change carefully. By holding a cold, dry 
bottle over the burning candle (Fig. i), a him of water 
gathers on the inside. Now if we remove the bottle, pour 
in some clear hmewater, and shake 
the bottle, the clear hquid becomes 
cloudy. This cloudiness is caused by 
a gas called carbon dioxide. Hence, 
the candle wax did not really " burn 
away." By burning in the air, the 
wax changed into water and carbon 
dioxide. 

The experiment just studied is an 
example of chemical change. Chem- 
istry is the science devoted largely 
to a study of chemical changes. 

2. Substances and properties. — The dilYercnt mate- 
rials involved in a chemical change are called substances. 
We are able to recognize and distinguish substances by 
characteristics called properties. Some properties 
readily detected, e.g. color, taste, odor, hardnes^ 
physical state {i.e. if solid, hquid 




Fig. 



Studying a 
chemical change 



and 



are 
the 



or 



gaseous ) 



Other 



PRACTICAL CHEMISTRY 



properties are found by measurement or special experiment, 
and are usually expressed by numbers, e.g. boiling point, 
melting point, conductivity of heat or electricity, and spe- 
cific gravity (i.e. relative weight). These properties, often 
called physical properties, are important, and we often use 
them in describing and recognizing substances. 

Very important, also, are chemical properties — the char- 
acteristics of substances revealed in chemical changes. 
Thus, iron rusts in the air but gold does not, copper dis- 
solves readily in nitric acid but platinum does not. Chemi- 
cal properties are the different items, so to speak, in the 

chemical conduct of 
substances. In chem- 
istry we pay special at- 
tention to chemical con- 
duct. 

3. What is the first 
characteristic of chemi- 
cal change ? — Let us 
answer this question by 
an experiment. Iron 
and sulphur are readily 
recognized. Besides 
their conspicuous prop- 
erties, sulphur dis- 
solves in carbon disulphide, and iron is attracted by 
a magnet. If we heat a mixture of iron powder and 
sulphur in a test tube (Fig. 2), the mass soon glows, and 
the glow often spreads and continues after the tube is 
removed from the flame. If we break the test tube 
and examine the product, we find that it is a hard, black 
solid, quite unlike either iron or sulphur. If we grind 
it in a mortar, and add a few drops of acid to a little of the 




Fig. 2. — Heating a mixture of iron and 
sulphur in a test tube 



CHEMICAL CHANGE ^COMPOUNDS — ELEMENTS 3 

powder, a gas with a bad odor is liberated. No such gas 
is produced when acid is added to the iron, the sulphur, 
or the mixture. Moreover, this black solid is not attracted 
by a magnet nor does it dissolve in carbon disulphide. 

Clearly a new substance has been formed. We may de- 
scribe the chemical change in chemical language. Two 
different substances, iron and sulphur, each with char- 
acteristic properties, have disappeared and a new substance 
called iron sulphide has been produced with properties 
different from the properties of the original substances. 
All chemical changes, however complicated, involve trans- 
formation of substances. So we may say : — 

Tlie first characteristic of chemical change is the forma- 
tion of one or more new substances from the original substance 
or substances. 

4. What is the second characteristic of chemical change ? 
— The experiment just considered may be done with more 
care. If we take the right proportions of iron and sulphur 
(7 of iron and 4 of sulphur), weigh each substance accu- 
rately, and heat the mixture until the chemical change is 
complete, we find that the weight of the iron sulphide is 
the same as the weight of the iron and sulphur together. 
Precise study has shown that this striking observation is 
true of all chemical changes. Hence, 

The second characteristic of chemical change is unchanged 
weight. 

5. An important law. — We see, then, as a result of our 
study, that in a chemical change substances are trans- 
formed but this transformation involves no change in the 
total weight of all the substances involved. This general fact 
about chemical change is often stated as the law of the 
conservation of matter : — 

No weight is lost or gained in a chemical change. 



4 PRACTICAL CHEMISTRY 

6. What is a substance ? — The word substance is often 
used in ordinary language to designate various kinds of 
materials. Thus, wood, cloth, paper, flour, soil, sugar, 
iron, and water are substances. But in chemistry the word 
substance means a kind of material which is alike through- 
out, i.e. all parts have the same properties. Moreover all 
specimens of a given substance have the same set of proper- 
ties. Sulphur is a substance. That is, every particle of 
sulphur is Uke every other particle, and different samples of 
sulphur are alike. Anything found in a specimen of sulphur 
that has different properties is another substance. It is 
called an impurity and the specimen of sulphur is called im- 
pure sulphur. 

7. What is a mixture? — ^ If we examine certain ma- 
terials, we find that they consist of two or more sub- 
stances, which can be easily recognized with the eye (or 
a magnifying glass) or can be separated by sifting, dis- 
solving, or filtering. A material which consists of sub- 
stances merely mixed or stuck together is called a mixture. 
Paint, milk, soil, granite, and muddy water are examples 
of mixtures. 

Mixtures have certain unmistakable characteristics. 
First, the ingredients of a mixture may vary in kind and 
proportion. Thus, soil may be largely sand, or clay, or 
organic matter. Indeed, the kind and proportion of in- 
gredients may vary widely and the mixture still have the 
same name. Second, the ingredients can be readily sepa- 
rated. For example, the preparation of flour consists 
mainly in separating the starch from the other parts of the 
ground kernel. Third, when we compare a mixture with a 
(chemical) substance, we find a marked difference. Every 
specimen and each part of a substance has the same proper- 
ties. But the properties of a mixture vary with the kind 



CHEMICAL CHANGE — COMPOUNDS — ELEMENTS 5 

and proportion of the ingredients. Obviously, a mixture 
of iron and sulphur may consist of any proportion of 
the ingredients, and the properties will depend on the 
proportion ; whereas iron sulphide is always alike through- 
out. 

8. Compounds and elements. — There are two classes 
of substances — compounds and elements. How are they 
related? If we heat strongly some red powder, called 
mercury oxide, in a test tube (Fig. 2), the powder turns 
dark and soon minute silvery drops collect on the upper 
part of the test tube. Now if we push well down into the 
test tube a joss stick with a glowing end, the glow increases 
and the end of the joss stick bursts into a flame. Clearly 
a gas is being produced which differs from ordinary 
air. 

The new substances formed from the red powder are the 
liquid, mercury, which can be seen, and the colorless gas, 
oxygen, which mingles with the air. Both substances 
are quite different from the original red solid, mercury 
oxide. Therefore, by heating we have transformed the 
substance, mercury oxide, into two different substances, 
mercury and oxygen. A chemical change has taken place. 
Mercury oxide has been decomposed into mercury and 
oxygen. Moreover, these new substances, mercury and 
oxygen, differ from mercury oxide in one fundamental 
property, viz. they cannot be decomposed. 

The relation of mercury and oxygen to mercury oxide is 
clear. Mercury and oxygen are the fundamental constit- 
uents of mercury oxide. We can decompose mercury oxide 
into its constituents, but there the decomposition stops. 
We have reached the end, chemically speaking. These two 
substances, mercury and oxygen, are not only simpler than 
mercury oxide, but they are examples of the simplest sub- 



6 PRACTICAL CHEMISTRY 

stances. Substances which have not yet been decom- 
posed by chemists into simpler substances are called ele- 
ments, whereas substances which can be decomposed into 
elements are called compounds. Obviously the compound 
mercury oxide consists of the elements mercury and oxy- 
gen. 

9. What are the characteristics of compounds? — Com- 
pounds have several essential characteristics. 

(i) The elements in compounds are chemically united. 
That is, the constituents of a compound are not merely 
mingled or lying side by side as in a mixture. They are 
held together by a force which is sometimes called chemical 
attraction. To separate a compound into its elem.ents, 
this attraction must be reduced or overcome chemically. 
Only by a chemical change can we decompose a compound 
into its elements or unite elements into a compound. 
Whereas a mixture can usually be separated into its in- 
gredients by some simple mechanical operation (7) . 

(2) The properties of compounds differ — often con- 
spicuously — from the properties of the elements that 
compose them. Thus, the blue sohd copper sulphate is 
composed of three elements — the red metal copper, the 
yellow sohd sulphur, and the colorless gas oxygen. 

(3) The most important characteristic of chemical com- 
pounds is their constant composition. This means that 
any given chemical compound always consists of an un- 
varying per cent of the same elements. For example, the 
compound water always contains 88.82 per cent of the 
element oxygen and 11. 18 per cent of the element hydrogen. 
This is an important fact in chemistry, so important that 
it is stated as the law of constant composition : — 

A chemical compound has a constant cofuposition by weight. 
This law will be studied again (98). 



CHEMICAL CHANGE — COMPOUNDS — ELEMENTS 7 



10. There is a large number of compounds. — The num- 
ber of compounds formed by various combinations of the 
elements is very large indeed, — too large for one person 
to study profitably. Fortunately, we can learn much 
about the essentials of chemistry by confining our study to 
the important elements and the best representatives of 
a few classes of compounds. 

11. More about elements. — There is only a small 
number of elements — about eighty-five. A complete 
table of the elements will be found on the inside of the 
back cover of this book. 

Important elements are shown in the accompanying 
table. 

T.\BLE OF Important Elements and Their Symbols 



Element 


Symbol 


Element 


Symbol 


Element 


Symbol 




Aluminium 


Al 


Gold 


Au 


Oxygen 





Barium 


Ba 


Hydrogen 


H 


Phosphorus 


P 


Bromine 


Br 


Iodine 


I 


Potassium 


K 


Calcium 


Ca 


Iron 


Fe 


Silicon 


Si 


Carbon 


C 


Lead 


Pb 


Silver 


Ag 


Chlorine 


CI 


Magnesium 


Mg 


Sodium 


Na 


Chromium 


Cr 


:Manganese 


Mn 


Sulphur 


S 


Copper 


Cu 


Mercury 


Hg 


Tin 


Sn 


Fluorine 


F 


Nitrogen 


N 


Zinc 


Zn 



Less than half of the elements are common. About 
98 per cent of the outer shell of the earth's crust consists 
of compounds derived from eight elements. The per cent 
of these elements is shown in the accompanying table. 

Table of the Composition of the Earth's Crust 



Oxygen 47.07 

Silicon 28.06 

Aluminium 7.90 



Iron 

Calcium . . . 
Potassium . 



4-43 
3-44 
2.45 



Sodium 2.43 

Magnesium 2.40 

Remainder 1.82 



8 



PRACTICAL CHEMISTRY 



Compounds in the ocean likewise consist of but few ele- 
ments, as appears from the following : — 

Table of the Approximate Composition of the Ocean 



Oxygen 85.79 

Hydrogen 10.67 

Chlorine 2.07 



Sodium 1. 14 

^Magnesium ... .0.14 
Sulphur 0.09 



Calcium 0.05 

Bromine 0.008 

Carbon 0.002 



The human body is a complicated structure, and yet the 
compounds in it are composed of but few elements; and 
some of these elements are in very small proportions. This 
fact is apparent from the illustrative table. 

Table of the Average Composition of the Human Body 



Oxygen 65.00 

Carbon 18.00 

Hydrogen 10.00 

Nitrogen 3.00 

Calcium 2 .00 



Phosphorus .... i.oo 

Potassium 0.35 

Sulphur 0.25 

Sodium 0.15 

Chlorine o. i ^ 



Magnesium 0.05 

Iron 0.004 

Iodine trace 

Fluorine trace 

Silicon trace 



It is evident from these tables that only a dozen elements 
are abundant. As a matter of fact a few elements by their 
various combinations furnish most of the substances studied 
in this book. The elements given in the above tables, in- 
deed most elements, do not occur free. That is, they do 
not occur singly but are combined with other elements in 
the form of compounds. Only a very few elements are 
found in the free, native, or uncombined state, e.g. sulphur, 
copper, gold, and carbon in the earth's crust, and oxygen 
and nitrogen in the atmosphere. 

12. Each element has a symbol. — Each element is desig- 
nated by an abbreviation called a symbol (11). Symbols 
are usually the first letter, or the first and a significant one, 
of the common name of the element. Thus, O is the symbol 



CHEMICAL CHANGE— COMPOUNDS -ELEMENTS 9 

of oxygen, C of carbon, CI of chlorine, Zn of zinc. In 
some cases the symbol is an abbreviation of a Latin name, 
e.g. Cu for copper {cuprum), Fe for iron ifcrrum), A^ for 
silver {argentum). All symbols, as we shall see later (105), 
have a very explicit meaning. They are used constantly, 
not only to designate elements and compounds l)ut also 
to express the relations of elements and compounds in 
chemical change. The symbol of each important element 
should be learned early in the study of chemistry. (See 
Exercise 11 at the end of this chapter.) 

13. Each compound has a formula. — Just as each 
element is designated by a symbol, so each compound is 
represented by a formula: A formula is a group of sym- 
bols — the symbols of the elements of which the compound 
is composed. Thus, FeS is the formula of the compound 
iron sulphide, HgO of mercuric oxide, CO2 of carbon dioxide, 
and H2O of water. Later we shall learn how formulas 
are derived. 

14. How chemical change, elements, and compounds 
are related. — In the chemical change involving iron and 
sulphur (3), these elements unite to form the compound 
iron sulphide. So also in the chemical change illustrated 
by the behavior of mercuric oxide (8), this compound 
decomposes into the elements mercury and oxygen. We 
cannot have a chemical change without involving one or 
more compounds. And in many cases elements, too, arc 
directly concerned. 

Chemical change is sometimes called chemical action. 
The term reaction, or interaction, is usually applied to a 
single chemical change. A reaction may be rei)resented 
in a condensed form, thus : — 

Sulphur + Iron = Iron Sulphide 
Such a condensed expression is called an equation. In 



lO PRACTICAL CHEMISTRY 

these simple equations, the plus sign may also be read and 
and the equality sign form {s). Thus, sulphur and iron form 
iron sulphide. Or in full, the elements iron and sulphur 
under suitable conditions undergo a chemical change which 
results in the formation of the compound iron sulphide. 

Since no weight is lost or gained in a chemical change 
(5), an equation can be used to represent this funda- 
mental fact. Experiment shows that 32 parts of sulphur 
always unite with 56 parts of iron. This fact is expressed 
as an equation thus : — 

Sulphur + Iron = Iron Sulphide 
32 56 88 

This equation is read; 32 parts of sulphur and 56 parts 
of iron form (or equal) 88 parts of iron sulphide. By parts 
we mean any denomination by weight, e. g. grams, kilo- 
grams, pounds, tons. 

EXERCISES 

1. State characteristic properties of (a) glass (&) gasolene, (c) water, 
{d) paper, (e) air, (/) lead. 

2. Define the term substance as used in chemistry. 

3. Give three illustrations of chemical change you have observed. 

4. State and illustrate the two characteristics of chemical change. 

5. State the law of the conservation of matter. What does the 
word conservation mean ? 

6. Name (a) five elements and {h) five compounds. 

7. What are some characteristics of a mJxture? Name three 
familiar mixtures. 

8. How can water be distinguished from gasolene? Copper from 
iron? Glass from sand? Air from illuminating gas? Sugar from 
starch? 

9. Name the eight most abundant elements in the earth's crust in 
their order. Give the symbol of each. 

10. What is an element? A compound? In what fundamental 
way do elements and compounds differ? Could you prepare (a) a 
compound from elements, {h) elements from a compound, (c) com- 
pounds from compounds, {d) elements from elements? 



CHEMICAL CHANGE — COMPOUNDS— ELEMENTS ii 

11. Learn the symbol of each element mentioned in this chapter. 
What is the formula of iron sulphide, water, mercury oxide, carbon diox- 
ide ? 

12. What is a reaction? An equation? Give an example of each. 

13. Interpret this equation : Mercury Oxide = Mercury + Oxygen. 

14. Make a list of all the new words in this chapter and defme each. 

15. State practical uses of chemistry in (a) the school building, 
(b) your home, (r) agriculture, (d) manufacturing processes in your 
city or town. 

PROBLEMS 

{The Metric System of Weights and Measures is constantly used in 
Chemistry and it should he learned or reviewed at once. See Appendix, §i.) 

1. What is the abbreviation of gram, centigram, liter, meter, cubic 
centimeter, decimeter, milligram, millimeter? 

2. Express (a) i liter in cubic centimeters, {b) 2 1. in cc, (c) i meter 
in centimeters, (d) 250 cm. in dm., (e) 1 kg. in grams, (/) 250 gm. in mg., 
(g) 56.75 1. in cc, (//) 1250 cc. in I., (/) i cc. in cu. m. 

3. How many cc. in (a) i liter, (b) 1 cu. dm., (r) i cu. m. ? 

4. If I m. of magnesium ribbon weighs 4 dg., how many mg. will 
5 cm. weigh? 

5. Into how many pieces 5 cm. long can a glass tube i m. long be 
cut? 

6. A flask holds 750 cc. Express its capacity in (a) 1., (b) cu. dm. 

7. A bottle holds exactly 1250 cc. (a) How many grams of water 
will fill it? (b) How many kg.? (c) How many 1.? 

8. Suppose exactly 3.5 gm. of iron and 2 gm. of sulphur are heated 
until the chem.ical change is complete. What weight of iron sulphide 
is produced? (Suggestion. See 5.) 

9. Suppose 5 gm. of iron and 2 gm. of sulphur are heated until the 
chemical change is complete, (a) What weight of iron sulphide is pro- 
duced? (b) Is any sulphur or iron left over? (c) If so, which and 
how much? 

10. What per cent of iron sulphide is sulphur? Iron? 

11. When mercury oxide is made, 25 parts by weight of mercury 
and 2 of oxygen unite. What is the per cent of (a) mercury and (b) oxy- 
gen in mercury oxide? 

12. How many grams of (a) hydrogen and (b) oxygen can be ob- 
tained from 150 gm. of water? (Suggestion. See 9 (3).) 



CHAPTER II 



OXYGEN 

15. Oxygen is an abundant and important element. — 
It forms nearly 21 per cent (by volume) of the atmosphere. 
Combined with hydrogen, it constitutes 88.82 per cent 
(by weight) of water ; combined with silicon and certain 

metals, it makes up nearly 
half of the earth's crust 
(11). Combined with car- 
bon, hydrogen, nitrogen, 
and other elements, it 
forms a large part of ani- 
mal and vegetable matter. 
Thus, the human body 
contains about 65 per cent 
of combined oxygen, while 
vegetable matter contains 
about 40 per cent. 

If the elements were 
to be named in order of 
importance, oxygen would 
be first. Without free 

oxygen animal life is impossible. It is also necessary in 

the famihar process of burning. 

16. Preparation of oxygen. — Among the first to pre- 
pare oxygen w^as the English scientist, Priestley (Fig. 3). 
He prepared it in 1774 by heating mercury oxide in much 
the same way as previously described (8). 




Fig. 3. — Priestley (i 733-1804) 



OXYGEN 13 



The gas can be prepared l)y decomposing other compounds of 
oxygen, such as potassium chlorate (KCIO3), lead oxide (PbOa), 
or barium oxide (BaO..). Thus, potassium chlorate — a compound 
of oxygen, chlorine, and potassium — when heated to a moderately 
high temperature yields all its oxygen, and a compound, potassium 
chloride (KCl), remains. 

Oxygen can also be prepared from water (HoO). When 
an electric current is passed through water which con- 
tains sulphuric acid or sodium hydroxide, two gases, oxygen 




Fig. 4. — A plant for manufacturing oxygen (and hydrogen) by 
passing an electric current through water containing sodium hydroxide 

and hydrogen, are liberated in separate tubes or compart- 
ments. This method is used to prepare oxygen (and hydro- 
gen) on a large scale (Fig. 4). When a small quantity is 
needed, it is prepared by dropping water upon sodium 
peroxide. 

17. Preparation of oxygen in the laboratory. — Oxygen 
is conveniently prepared in the laboratory by heating a 
mixture of potassium chlorate and manganese dioxide 
in the apparatus shown in Fig. 5. A mixture of about four 



14 



PRACTICAL CHEMISTRY 




parts of potassium chlorate and one part of manganese 
dioxide is put in the test tube A and gently heated. 

The oxygen escapes 
through the delivery 
tube D into bottles 
previously filled with 
water and inverted 
over the end of the 
tube in the pneumatic 
trough. The oxygen 
bubbles up into the 

Apparatus for preparing oxygen ^^^^^^ ^^^ displaces 
in the laboratory 

the water. 

18. The preparation of oxygen illustrates chemical 
change. — The chemical change consists in the decompo- 
sition of the compound potassium chlorate into the element 
oxygen, and the compound potassium chloride. This 
chemical change may be expressed by this equation : — 

Potassium Chlorate = Oxygen + Potassium Chloride 

(Potassium-Chlorine-Oxygen) (Potassium-Chlorine) 

Chemical changes like this are common, and the 
term decomposition is applied to them. Decomposition is 
chemical change in which a compound is separated chemi- 
cally into other substances which are elements or com- 
pounds. 

19. Properties of oxygen. — Pure oxygen has no color, 
odor, or taste ; certain impurities may give a slight odor and 
taste to the gas prepared in the laboratory. It is not very 
soluble in water, and for this reason can be collected over 
water. Oxygen is slightly heavier than air. One liter of oxy- 
gen weighs 1.43 grams, if carefully measured and weighed at 
the temperature of o degrees as registered by a centigrade 



OXYGEN 



15 



n 



m 



thermometer and also under a pressure of 760 millimeters 
as registered by a barometer (or briefly at 0° C. and 760 
mm.). This value — 1.43 grams — should be remembered. 
20. The chemical conduct of oxygen is conspicuous. — 
Oxygen forms compounds with most elements. It also in- 
teracts chemically with many compounds. 
This combining or interacting is often strik- 
ing on account of the accompanying Hght 
and heat. At ordinary temperatures oxy- 
gen unites slowly with many elements. 
Thus, metals, such as lead, zinc, and cop- 
per, tarnish or rust slowly, i.e. they com- 
bine slowly with the oxygen of the air. 
With phosphorus, however, the chemical 
action is quite rapid, as may be seen by p^^ 6.^^^1phur 
the glow and fumes when the end of a burning in a 
phosphorus- tipped match is rubbed, espe- bottle of oxygen 
cially in the dark. 

The chemical activity of oxygen at temperatures above the ordi- 
nary is readily shown by putting burning or glowing substances into 
the gas. The action, scarcely noticeable in air, 
becomes energetic, and the substances burn rapidly 
and brilliantly. Thus, a glowing splint of wood or 
piece of charcoal when put into a bottle of oxygen 
bursts immediately into flame. Sulphur burns in 
air with a feeble bluish flame, but in oxygen the 
Clt^ flame becomes large and brilliant (Fig. 6). Iron 

/ \ can hardly be made to burn in air, but if steel wool 

(matted strands of iron) is merely heated and thrust 
into a bottle of oxygen, the iron burns, sends off a 
shower of sparks, and often forms drops of molten 
iron which crack the bottle (Fig. 7). 



Fig. 7. — Iron 
burning in a 
bottle of oxy- 
gen 



In the experiments just described, we 
should note especially that the oxygen itself 



i6 PRACTICAL CHEMISTRY 

does not burn. Rather it assists burning. So if we were 
to state briefly the chemical conduct of oxygen, we would 
say oxygen does not burn but assists the burning of other 
substances. The chemical conduct of oxygen described 
above is sometimes called its chief chemical property. 

21. Test for oxygen. — The critical examination made 
to estabhsh the identity of an element or compound is 
called testing or making a test. The behavior of a sub- 
stance under stated conditions is called the test for the sub- 
stance. Thus, the test for oxygen is its chief chemical con- 
duct, viz. the gas does not burn, but assists burning at 
elevated temperatures. 

22. The chief chemical property of oxygen illustrates 
chemical change. — In the experiments described in 20, 
one feature is conspicuous, viz. the disappearance of the 
original substances and the formation of new substances. 
The chemical change in the case of the carbon, sulphur, and 
iron is the combining of oxygen with these elements. The 
oxygen unites with each element, and the product is a com- 
pound of the two elements. This kind of chemical change 
illustrates combination, and can be expressed by an equa- 
tion. Thus : — 

Carbon -j- Oxygen = Carbon Dioxide 

(Carbon-Oxygen) 

Combination is chemical change in which compounds are 
formed by the union of two or more substances. 

23. Oxidation and oxides. — The special terrn oxida- 
tion is applied to those cases of combination in which oxygen 
is the combining element. Substances which furnish the 
oxygen are oxidizing agents. Free oxygen and air are 
oxidizing agents, though the oxygen for oxidation is often 
provided by compounds of oxygen, especially those that 
yield oxygen readily, such as potassium chlorate. The 



OXYGEN 17 

compound formed by the union of oxygen and another ele- 
ment is called an oxide of that element. Thus, carbon 
forms carbon dioxide. 

Oxides of different elements are distinguished by placing 
the name of the element (or a slight modification of it) 
before the word oxide, e.g. magnesium oxide, nitric oxide. 
Sometimes di-, or a similar numerical syllable, is prefixed 
to the word oxide, e.g. manganese dioxide (MnO^), sul- 
phur trioxide (SO3), phosphorus pentoxide (P2O5). Many 
familiar substances are oxides, e.g. water is hydrogen oxide 
(H2O), lime is calcium oxide (CaO), sand is siUcon dioxide 
(SiO^X red lead is lead tetroxide (Pb304), and the most 
abundant iron ore is iron oxide (FcoOs). 

24. Oxidation of compounds. — Oxidation is by no 
means limited to elements. Many compounds burn readily, 
i.e. combine as a whole with oxygen. Thus, carbon monox- 
ide (CO) unites directly with oxygen to form carbon diox- 
ide (CO2). 

Oxidation is an important chemical change. Later we 
shall find that the term includes other kinds of chemical 
action. 

25. Combustion is oxidation. — During oxidation heat 
is liberated, and if the heat is intense, hght is also produced. 
Different substances react with oxygen, i.e. oxidize, at dif- 
ferent rates. If oxidation is slow, as in the rusting of some 
metals, the temperature may not rise appreciably, because 
the heat escapes about as fast as it is liberated. If oxida- 
tion is rapid, heat is liberated quickly, the temperature 
rises suddenly, and the substance burns, often with dazzhng 
light. This rapid oxidation that produces heat and Ught 
is called combustion. In ordinary language combustion 
means fire or burning ; in chemical language it is rapid 
oxidation. 



i8 



PRACTICAL CHEMISTRY 



Sometimes the heat Hberated during slow oxidation cannot es- 
cape readily, but accumulates, hastens the oxidation, and finally the 
temperature rises to such a point that the substance takes fire. Thus, 
oily rags carelessly thrown aside by painters, moist hay stored in a 
poorly ventilated barn, and soft coal kept in a pile a long time in 
the air or in the w^arm hold of a ship sometimes take fire without 
apparent cause. Such fires, often unexpected and disastrous, are said 
to be due to spontaneous combustion, though they are simply cases 
of slow oxidation which becomes accelerated by accumulated heat. 

26. Combustion was first interpreted by Lavoisier. 

— Simple as it is, the answer to the question " What hap- 
pens when a substance 
burns? " was not made 
quickly. Indeed, ' several 
famous chemists tried to 
answer this fascinating 
question and their com- 
bined work extended over 
about a century. The 
answer was delayed many 
years by a false theory 
called the phlogiston 
theory. The advocates of 
this theory believed that 
'' combustible substances 
contain a principle called 
phlogiston, and that when 
a substance burns, phlogiston escapes." This is false. But 
it was not until about 1775 that the French chemist' Lavoi- 
sier (Fig. 8) proved by his own and others' experiments: 
(i) that phlogiston did not exist, and (2) that ordinary 
combustion is a process of combining with " a certain sub- 
stance contained in the air." Soon after, he showed that 
this *' substance " is identical with the gas discovered by 




Fig. 8. — Lavoisier (i 743-1 794) 



OXYGEN 



19 




Fig. 9. — Apparatus used by La- 
voisier in his famous experiment 
on combustion 



Priestley in 1774. In 1778 Lavoisier named the gas 
oxygen. 

So important is Lavoisier's discovery we must consider 
it in detail. 

Previous to Lavoisier's time it had been shown that air is 
necessary for combustion. It had also been shown that 
when a substance burns in 
air, the product weighs more 
than the original substance. 
Lavoisier himself verified this 
second observation by care- 
ful experiments. He knew, 
then, these two simple facts 
about combustion: d) air 
is necessary and (2) the 
weight increases. Still, the 
question to be answered was, '' What happens when a sub- 
stance burns?" Lavoisier answered the question by a 
conclusive experiment (Fig. 9). 

He put mercury in the retort having a long neck which communi- 
cated with the jar. The jar contained air confined over mercury in 
the larger lower vessel. Having arranged the apparatus so that the 
mercury in the retort was in contact with the air in both the retort and 
jar, he heated the retort by means of the furnace and kept the mer- 
cury in the retort just below the boiling point for twelve days. When 
the apparatus was cold, he noticed two things : (i) A red powder had 
accumulated on the surface of the mercury in the retort, and (2) the 
air in the retort and jar had decreased in volume about one fifth. 

He collected the red powder, put it in a glass vessel, heated it 
intensely, collected the gas, and measured its volume. He found the 
volume was the same as the decrease in the volume of the original 
air inclosed in the apparatus. He tested this gas, and found it had 
the properties of the gas previously obtained by Priestley, especially 
the property of making a lighted candle burn vigorously. Also he 
tested the gas left behind in the retort and jar and found that it ex- 



20 PRACTICAL CHEMISTRY 

tinguished a lighted candle. From these facts Lavoisier concluded : 
(i) that air contains a gas which is removed by heating substances 
in it, (2) that this gas is about one fifth of air, (3) that this gas unites 
with substances in the process called combustion or burning, and 
(4) that this gas is identical with the gas obtained by Priestley from 
his " red precipitate of mercury." 

We might summarize Lavoisier's work thus : oxygen is 
the gas in the air that is necessary for combustion. 

27. Oxygen is essential to life. — Free ox>^gen is essen- 
tial to all forms of animal Hfe. If human beings or animals 
are deprived of air, they die. In breathing, air is drawn 
into our lungs ; here the oxygen of the air is taken up by 
the blood, which distributes it to all parts of the body. 
This oxygen slowly oxidizes the tissues of the body. By 
this slow oxidation, waste products are formed and heat is 
suppHed to the body. Two of these waste products are 
carbon dioxide gas and water vapor, which are exhaled 
from the lungs ; water vapor is also given off through the 
skin. New tissue is built up from the food we eat. 

The human body resembles a steam engine. In each, the oxygen 
of the air helps burn fuel largely composed of carbon. In the engine, 
the products escape through a chimney, and the heat produced by 
the chemical change is used to form steam, which moves parts of the 
machine. In the body, the products escape through the lungs and 
other organs, and the heat keeps the body at the temperature at which 
it can best perform its functions. 

28. Manufacture and uses of oxygen. — Oxygen for 
industrial and scientific use is manufactured by decompos- 
ing water by an electric current (16) or by separating air 
into its components (128). The gas is stored under pres- 
sure in strong metal tanks (Fig. 10). 

A mixture of oxygen and hydrogen or acetylene, if 
burned in a suitable apparatus, produces an intensely hot 
flame. The oxy-hydrogen flame is used to melt certain 



OXYGEN 



21 




Fig. lo. — A tank 
of oxygen 



metals and to produce the intense light of the stereopticon, 
while the oxy-acetylene flame finds appUcation in welding 
and in burning apart heavy steel structures, 
e.g. girders of bridges (57, 334). 

Oxygen is often administered to persons 
who are too ill or weak to inhale the ordi- 
nary volume of air. In submarine boats 
the oxygen of the air used up is replaced 
by oxygen released from tanks. Airplanes 
are often equipped with an oxygen tank 
and breathing apparatus to supply quickly 
the oxygen needed by the aviator at eleva- 
tions where the air is rarefied. 

29. Saving lives by oxygen apparatus. — 
Oxygen is used in various forms of breath- 
ing apparatus for rescue work. The pulmotor, or lung- 
motor, is essentially a pump by which air rich in oxygen 
can be forced into the lungs at intervals approximating 
the normal rate of breathing. The pulmotor is used to 
resuscitate persons who have been overcome by smoke or 
poisonous gases (e.g. illuminating gas) or who have been 
rendered unconscious by drowning or by an electric shock. 
Fire departments, poKce officials, and public health officers 
are suppUed with pulmotors for emergencies. 

Another form of rescue apparatus can be hung from the 
shoulders like a knapsack. The man's head in one type 
is covered with a leather helmet ; in a more recent type 
the man's nose is clipped so he must breathe through his 
mouth (Fig. ii). Flexible tubes connect his mouth with 
a breathing bag (right), a cyUnder of compressed oxygen 
gas and a regenerating can (left) ; the latter contains po- 
tassium hydroxide to absorb the water vapor and carbon 
dioxide exhaled from the lungs. The amount of oxygen 



22 PRACTICAL CHEMISTRY 

needed by the wearer (as well as the circulation of the 
gases) can be regulated by a valve on the cylinder ; the 
nitrogen originally inhaled and in the apparatus at first is 





^ «r^^^P^ 


f 




1 


JH 


k'^i 


■i^ 


mi 


B^ 


JP 


■L^ M 


t| 


,m 


^^® 


m 




i 


Ik 


n 



Fig. II. — Man equipped %Yith oxygen-breathing apparatus. He 
breathes through his mouth from the gas bag carried on his chest 
(right). The tank of oxygen and the regenerating can are carried 
on his back (left) 

breathed over and over. The cyHnder contains enough 
oxygen for about two hours. 

A man provided with an oxygen-breathing apparatus 
can safely enter places where the air contains smoke or 
poisonous gas, and make repairs, extinguish fires, or res- 
cue workmen who have been overcome. Extensive use 
is made of this kind of rescue apparatus in mine disasters. 

30. Ozone. — Ozone is a gas related to oxygen. It is formed from 
oxygen when electric sparks pass through air, e.g. during a thunder 
storm. It is also formed near electrical machinery, and is prepared 
on a commercial scale by a silent electrical discharge, i.e. in a special 
kind of machine which permits a discharge without sparks. 

Ozone changes back into oxygen — slowly at ordinary temperatures 
and rapidly at high temperatures. Hence ozone is a good oxidizing 
agent. It is sometimes used to bleach {i.e. whiten) flour, starch, oils, 



OXYGEN 23 

waxes, and wool. Its main use is to destroy bacteria in drinking water, 
especially in certain European cities. 

EXERCISES 

1. Prepare a brief summary of this chapter. 

2. What is the characteristic chemical property of oxygen? 

3. If air contains a large proportion of another gas besides oxygen, 
how must the general properties of this other ingredient compare with 
those of oxygen? 

4. Make a list of the new chemical words in this chapter and de- 
fine each. 

5. (a) Make a list of the name and symbol of each element men- 
tioned in studying oxygen, (b) Make a list of the compounds men- 
tioned in this chapter and the elements in each, (c) Learn the for- 
mula of each compound (as given). 

6. What general chemical change is involved in ordinary burning? 
What class of chemical changes is illustrated by (a) preparation of oxy- 
gen from mercuric oxide, (b) burning of sulphur in oxygen? 

7. Cite cases of spontaneous combustion of which you have heard 
or read. Suggest methods to prevent spontaneous combustion of 
(c) oily rags, (b) coal, (c) hay. 

8. Devise an experiment to show that air contains oxygen. 

9. Topics for home study, (a) Why does a draft of air make a 
fire burn \vell? (b) A draft of air often extinguishes a candle flame. 
Why? (c) What oxides are found in the home? (d) How do fish 
obtain oxygen ? 

10. What chemical part does oxygen take in : (a) respiration, 

(b) burning, (c) combustion, (d) oxidation, (e) kindling a fire? 

11. Define (a) oxidation and (b) oxide. Name five oxides. 

12. Essay topics : (a) Uses of oxygen, (b) Discovery of oxygen. 

(c) Priestley, (d) Oxygen and life, (e) Combustion. (/) Lavoi- 
sier, (g) Extinguishing fires. 

PROBLEMS 

1. (a) What is the weight in gm. of 35 1. of oxygen? (6) Of 
35,000 cc? (c) Of 35 cubic decimeters? 

2. How many gm. of oxygen are in a bottle holding 2.5 1. (at 0° C. 
and 760 mm.) ? 

3. A pupil prepared enough oxygen to fill a tank holding i cu. m. 
(at 0° C. and 760 mm.). How many gm. were prepared? 

4. (a) How many liters (at 0° C. and 760 mm.) will 25 gm. of 
oxygen occupy? (b) How many gm. will 25 1. of oxygen weigh? 



24 PRACTICAL CHEMISTRY 

5. How many gm. of oxygen (at o° C. and 760 mm.) in a cylindri- 
cal gas holder which is i m. high and 30 cm. in diameter? 

6. If air contains 21 per cent of oxygen by volume, how many gm. 
of oxygen can be extracted from 950 1. of air? 

7. A pupil prepared five bottles of oxygen, each holding 250 cc. 
(at 0° C. and 760 mm.). How many gm. of oxygen were prepared? 

8. Water contains 88.82 per cent of oxygen. Suppose 0.5 kg. 
was decomposed, how many liters of oxygen (at 0° C. and 760 mm.) 
were formed? 

. 9. A room is 10 m. long, 5 m. wide, and 4 m. high. How many gm. 
of water must be decomposed to furnish enough oxygen (at 0° C. and 
760 mm.) to fill the room? 

10. Potassium, chlorate contains 39.18 per cent of oxygen. If 35 gm. 
are heated, (a) how many gm. of oxygen are liberated, and (b) how many 
bottles each containing 250 cc. will the gas fill? 



CHAPTER III 
CARBON AND ITS OXIDES 

31. Carbon is an important and useful element. — Like 
oxygen, the element carbon is found both free and com- 
bined. Free carbon is famiUar as the black soUd that makes 
up the greater part of the common substances coal, char- 
coal coke, and lampblack. The soft, slippery, shiny 
solid called graphite is also largely carbon. And. strange 
as it may seem, the valuable gem called diamond is also 
carbon — pure crystalline carbon. 

Coal, charcoal, and coke are fuels. Lampblack is made 
into printing ink and black paint. The various varieties 
of these three forms of carbon are used in many chemical 
industries, e.g. the manufacture of iron and steel. Graphite 
is made into the 'Mead" of lead pencils, stove polish, lubri- 
cants, crucibles (for melting metals), and electrodes (for 
electric furnaces and electrolytic cells (497, 512)). Impure 
diamond is used to poKsh pure diamond and other gems, to 
cut glass, and as the cutting part in the diamond drill that 
is used to bore wells for oil and water and to drill hard 
rocks. 

32. Carbon forms an extraordinarily large number of 
compounds. — The natural and manufactured compounds 
of carbon number over 200,000. These compounds are 
so numerous they are treated by themselves in a branch 
of chemistry called Organic Chemistry. Carbon is the 
fundamental element of plant and animal life. Compounds 
composed of carbon, hydrogen, and oxygen, and in some 

25 



26 PRACTICAL CHEMISTRY 

cases also of nitrogen, form such common substances as 
sugar, starch, fat, cotton, paper, flour, rubber, soap, wool, 
and meat. With hydrogen it forms a large class of com- 
pounds called hydrocarbons, which are found in illumi- 
nating and fuel gases, petroleum, kerosene, gasolene, lubri- 
cating oils, paraffin wax, and turpentine. The manufac- 
tured compounds of carbon include dyes, medicines, per- 
fumes, and a vast number of other substances. 

The commonest inorganic compounds — those usually 
considered in the branch of chemistry we are studying — 
are the carbonates and the oxides. The carbonates are 
compounds of carbon, oxygen, and a metal such as calcium, 
magnesium, or sodium. Thus, calcium carbonate (CaCOs) 
is the natural substance called limestone, marble, or chalk. 
Sodium carbonate (NasCOs) is the common substance 
washing soda. There are two carbon oxides — carbon diox- 
ide (CO2) and carbon monoxide (CO). 

In later chapters we shall consider more fully, carbon 
and some of its important compounds. In this chapter 
we shall Umit our study to carbon and its two oxides. 

33. Formation of carbon dioxide. — We have already 
seen that carbon dioxide is formed when carbon burns in 
oxygen and also when a candle burns in air (20, 1). These 
are examples of a common chemical change, viz. the for- 
mation of the compound carbon dioxide when the element 
carbon, or a combustible compound of carbon, burns in 
oxygen or in air. 

We have also found that the process called burning or 
combustion consists usually in the union of carbon (and 
also, of course, hydrogen, if present) with oxygen (25, 26). 
This means that carbon dioxide is being constantly formed 
by the burning of such common fuels as wood, paper, coke, 
coal, charcoal, oil, and gas. In fact, carbon dioxide is 



CARBON AND ITS OXIDES 



27 




A 



always one of the products of combustion, as they are often 
called, yielded by burning any substance which contains 
carbon, e.g. sugar, starch, wax, meat, milk, camphor, 
alcohol, oil, dyes, fat, and drugs. The presence of carbon 
dioxide can be shown by bubbling the products of com- 
bustion, e.g. smoke, through Umewater (1). 

Reference was made in 27 to the digestion of food. One 
of the products of this complex process is carbon dioxide. 
This means in simple language that the 
element carbon, which is one of the con- 
stituents of our food, is oxidized to carbon 
dioxide. Heat is liberated when carbon is 
oxidized, and this chemical change is one 
part of the continuous and complicated 
process by which our bodies keep uni- 
formly warm. The two main products cf 
digestion are exhaled from^ the lungs. The 
presence of carbon dioxide in exhaled 
breath may be readily shown by blowing 
the breath gently through a glass tube into 
a bottle containing limewater (Fig. 12). 
The Uquid becomes milky, owing to the 
reaction between the carbon dioxide and 
the Umewater. Limewater contains cal- 
cium hydroxide, which reacts with the carbon dioxide and 
forms the white insoluble compound calcium carbonate. 
This chemical change is a test for carbon dioxide (from 
any source). We express the chemical change thus : — 

Carbon Dioxide -h Calcium Hydroxide = Calcium Carbonate-f Water 

(Carbon-Oxygen) (Calcium-Hydrogen- (Calcium-Carbon-Oxypcn) (Hydro- 

Oxygen) gen-Oxygen) 

Carbon dioxide is also formed by other chemical changes, 
such as the decay of many kinds of animal and vegetable 



Fig. 12. — Blow- 
ing through 
limewater to 
show the pres- 
ence of carbon 
dioxide in the 
breath 



28 



PRACTICAL CHEMISTRY 



matter and fermentation of organic substances like sugar. 
The latter process is illustrated by the liberation of carbon 
dioxide during the raising of bread. 

34. Preparation of carbon dioxide. — We can prepare 
carbon dioxide by burning carbon, or a combustible com- 
pound of carbon, in oxygen or air, but the gas could not 
be conveniently separated from the smoke or the other 
gases, such as the unused oxygen or the nitrogen (in the air). 
On a large scale, however, the gas is prepared by passing 
air over hot coke, purifying the gaseous product, and finally 
extracting the carbon dioxide by a special cooling process. 

In the laboratory carbon dioxide is most conveniently prepared 
by the interaction of an acid and a carbonate. Dilute hydrochloric 

acid and calcium carbonate (in 
the form of marble chips) are 
usually used. When the acid 
is poured on the calcium car- 
bonate, the gas is rapidly lib- 
erated. The apparatus shown 
in Fig. 13 can be used for this 
experiment. Calcium carbonate 
is put in the bottle A and the 
dilute hydrochloric acid is in- 
troduced through the dropping 

tube B by pressing the clamp. 

Fig. 13. — Apparatus for preparing 1. i- • 1 4. 

u A- -A f -A ^r.A The carbon dioxide passes out 

carbon dioxide from acid and ^ 

marble in the laboratory through the delivery tube D 

into the pneumatic trough, bub- 
bles up into the bottles (previously filled with water), and displaces 
the water. The bottles when full of gas are immediately removed 
and covered with filter paper or a glass plate. 

35. Some experiments with carbon dioxide. — If several bottles of 
carbon dioxide are collected, we can perform experiments which will 
give us information about the properties of this gas. 

(i) A blazing joss stick or splinter of wood, if plunged into a bottle 
of carbon dioxide, is immediately extinguished. (2) If we lower a 
short, lighted candle into a bottle of air and quickly invert a bottle of 




CARBON AND ITS OXIDES 



29 




carbon dioxide loosely over it, the gas falls down upon the candle 
which is soon extinguished. (3) When we fill a bottle of carbon diox 
ide one third full of water, cover it tightly with the hand, shake vigo 
rously a minute or two, then invert the bottle in 
a dish of water, and remove the hand, water 
rushes up into the bottle. 

36. Some properties of carbon dioxide. 

— Carbon dioxide is a colorless and 

odorless gas. It is heavier than air — 

about 1.5 times heavier. A hter of the 

pure gas weighs 1.98 grams (at 0° C. and 

760 mm.). It dissolves in water. At 

ordinary temperature and pressure, water 

dissolves about its own volume of carbon 

dioxide. Under increased pressure the 

solubihty increases, but the gas escapes 

when the pressure is lessened. Soda water is manufactured 

by dissolving carbon dioxide under pressure in water ; 

hence when soda water is drawn 
from a soda fountain or siphon 
(Fig. 14), the water bubbles and 
forms a froth, owing to the escape 
of the gas under diminished pres- 
sure. Many beverages, such as 
ginger ale, are "carbonated," i.e. 
they are manufactured by forcing 
carbon dioxide into the prepared 
liquid ; the bottle is closed tightly 
with a cork or cap. When the 
bottle is opened, the gas which 



Fig. 14. — A siphon 
of soda water 




escapes (Fig. 15) will turn lime- 



Fig. 15. — E.xperiment to 
show that carbon dioxide 
escapes from a carbonated water milky ; hence the gas is 
beverage carbon dioxide. 



30 PRACTIC\L CHEMISTRY 

37. Liquid and solid carbon dioxide. — Unlike oxygen, carbon diox- 
ide can be readily liquefied and solidified. If enough pressure is 
applied at ordinary temperatures, the gas becomes a liquid. Liquid 
carbon dioxide is stored and sold in strong steel tanks. If the tank 
is properly opened, part of the escaping liquid by evaporating quickly 
removes so much heat that the remainder becomes white, snowlike, 
soHd carbon dioxide. 

38. Chemical conduct of carbon dioxide. — In our ex- 
periments we noticed that carbon dioxide, unlike oxygen, 
did not assist combustion. Nor did it burn. This nega- 
tive behavior, so to speak, is sometimes called inertness. 
We may say, then, that carbon dioxide is an inert gas. 
However, it does react with some substances. Thus, it 
combines with water to form a compound called carbonic 
acid ; but this compound is not stable, i.e. it decomposes 
readily and re-forms the water and carbon dioxide. 

We have called attention several times to the reaction in 
which carbon dioxide and Hmewater form calcium carbonate 
and water. This chemical change, we have also said, serves 
as a test for carbon dioxide. A similar reaction takes place 
between carbon dioxide and sodium hydroxide. The prod- 
uct, in this case, however, is sodium carbonate. Sodium 
carbonate is soluble in water and the solution feels slippery, 
like soap ; in fact, sodium carbonate is sometimes called 
washing soda and is used in large quantities as a cleansing 
agent. Sodium bicarbonate is closely related to sodium 
carbonate. Sodium bicarbonate is cooking soda. Alone, 
or as an ingredient of baking powder, it is widely used in 
cooking because it gives off carbon dioxide which puffs 
up the dough. 

39. Relation of carbon dioxide to life. — Carbon diox- 
ide is not poisonous, though the presence of a small quan- 
tity in the air of a room is objectionable. As already 
stated, the carbon dioxide that is exhaled from our lungs 



CARBON AND ITS OXIDES 



31 



is one of the products formed by the oxidation of the tis- 
sues of the body, new tissue itseh* being formed from the 
food (27). The carbon needed for the 
rebuilding of tissue is supphed by 
starch and other substances we eat. 
Carbon dioxide is a waste product of 
animal life. 

On the other hand, carbon dioxide 
is an essential food of plants. Through 
their leaves, especially, they absorb 
carbon dioxide from the atmosphere, 
decompose it. reject part of the oxygen, 
and store up the carbon in the form of 
complex compounds, such as starch. 
The sunlight and the green coloring 
matter (called chlorophyll) aid the 
plant in the formation of these com- 
pounds. 

The relation of carbon dioxide to life 
is clear. Plants absorb carbon dioxide 
and transform, it into starch, whereas 
animals eat starch as food, assimilate 
it. and oxidize the carbon to carbon 
exhaled into the atmosphere ready for 
and so on. 




Fig. 16. — Experiment 
showing the absorp- 
tion of carbon diox- 
ide and liberation of 
oxygen by plants 

dioxide, which is 
the plants again. 



The fact that plants take up carbon dioxide and reject oxygen 
can be readily illustrated, as shown in Fig. 16. Fresh green leaves 
are put into the flask, which is then completely tilled with water satu- 
rated with carbon dioxide. The stopper with its funnel is pushed in 
to exclude the air. the funnel is partly filled with the same liquid, and 
the test tube is filled and arranged as shown in the figure. On ex- 
posure to the sunHght for several hours, a gas collects in the test tube. 
The usual test shows that the gas is oxygen (21). Xo oxygen is 
produced if water free from carbon dioxide is used. 



32 



PRACTICAL CHEMISTRY 



The significant relation of carbon dioxide and oxygen 
to plants and animals, which is often spoken of as the cycle 
of carbon and oxygen, is shown in Fig. 17. 



Carbon dioxide 
in the air 

0\ 



Animals 




Animals 



Carbon dioxide 
in the air 



Fig. 17. — Cycle of carbon (.4) and oxygen (B) 

40. Carbon dioxide and fire extinguishers. — Carbon 
dioxide does not burn, but extinguishes burning substances. 
Instead of the gas itself, a saturated solution is frequently 
used to put out small fires. The solution is prepared, as 





r~i ^m^ 








r 
r 




'm 


h 


—JMt^§mSSSS 




'^^'^- ■ 



Fig. 18. — Special type of motor chemical engine for extinguishing forest 
fires and grass fires. Two large generating tanks are on top and 
portable extinguishers are on the running board 

needed, in portable fire extinguishers and in chemical en- 
gines (Fig. 18) by the interaction of sulphuric acid and 
sodium bicarbonate. The ordinary fire extinguisher con- 
tains a solution of sodium bicarbonate and a loosely stop- 



CARBON AND ITS OXIDES 



33 




percd bottle of sulphuric acid ; upon inverting the tank, 
the stopper of the acid bottle falls out, the two liquids 
mix, and the pressure of the generated gas forces the satu- 
rated solution of carbon dioxide out of the nozzle of the 
extinguisher ; some of the carbon dioxide 
itself escapes (Fig. '19). The water solu- 
tion of carbon dioxide together with the 
gas forces the oxygen of the air away 
from the fire and thereby reduces or en- 
tirely prevents combustion. 

41. Carbon monoxide differs from car- 
bon dioxide. — Carbon monoxide is a 
compound of carbon and oxygen, but 
the two compounds differ in properties 
and composition. They can be prepared 
from each other by chemical processes. 

Carbon monoxide, Hke carbon dioxide, 
is a gas without color, odor, or taste. 
But in other properties the two gases 
differ. Thus, carbon monoxide is only 
slightly soluble in water, and does not 
form a compound with water. It is 
lighter than carbon dioxide; a hter weighs 1.25 gm. 

42. Carbon monoxide is poisonous. — Carbon monoxide 
is a dangerous poison because the lack of odor prevents 
its detection. A small fraction of a per cent of this gas 
in the air produces a stupefying effect. Many deaths have 
been caused by breathing air containing it. Carbon monox- 
ide impoverishes the blood by forming a compound with 
one of its constituents, and persons who have been poisoned 
by this gas cannot usually be revived by air, as in the case 
of suffocation by carbon dioxide. It is an ingredient of 
ordinary illuminating gas, and care should always be taken 



Fig. 19. — Portable 
fire extinguisher 
(partly open) 
showing stop- 
pered acid bottle 
in original posi- 
tion 



34 PRACTICAL CHEMISTRY 

to prevent the escape of illuminating gas (as well as the 
gas from a coal stove or furnace) into rooms occupied by 
human beings. The exhaust gases from an automobile 
engine contain carbon monoxide, and special care should be 
taken to ventilate a small garage. The pulmotor is often 
used to revive persons who have been overcome by gases 
containing carbon monoxide (29). 

43. Chemical conduct of carbon monoxide. — Carbon 
monoxide, unhke the dioxide, burns in air or oxygen. The 
flame is blue. The product is carbon dioxide. The equa- 
tion for this chemical change is : — 

Carbon Monoxide + Oxygen = Carbon Dioxide 

(Carbon-Oxygen) (Carbon-Oxygen) 

The flickering bluish flame often seen on the top of a coal 
fire is caused by the burning carbon monoxide. 

Not only does carbon monoxide unite readily with 
oxygen, but it withdraws oxygen from hot oxides ; carbon 
itseK acts in the same way. In chemical language carbon 
monoxide (and also carbon) is a reducing agent; i.e. it 
withdraws oxygen from compounds. This chemical re- 
moval of oxygen is called reduction. In the manufac- 
ture of iron from iron ores, the ore, which is an oxide 
(FeoOs), is reduced by carbon monoxide in a blast furnace, 
the gas for this purpose being produced by the incomplete 
combustion of coke. The same kind of chemical change 
takes place easily with copper oxide and hydrogen (55). 

44. The two carbon oxides are formed in a coal fire. — 
The oxygen of the air entering at the bottom of a coal 
fire combines with the hot carbon of the coal and forms 
carbon dioxide — the first change. But the carbon diox- 
ide in passing up through the upper layer of hot coal is 
reduced by the carbon to carbon monoxide — the second 



CARBON AND ITS OXIDES 



35 




20. — Carbon oxides are 
formed in a coal fire 



change. The carbon monoxide escapes through the top 
of the tire into the air, where much, or all, of it burns 
to carbon dioxide — the third 
change. Therefore we see that 
the two oxides are closely re- 
lated chemically and pass into 
one another readily, especially 
in a coal fire (Fig. 20). 

45. Formation and preparation of 
carbon monoxide. — Carbon mon- 
oxide is always formed when carbon 
and certain carbon compounds {e.g. 
gasolene) burn in a limited supply 

of air. It is also formed when steam is passed through a hot fire of 
hard coal or coke. The gaseous product is a mixture of carbon mon- 
oxide and hydrogen ; this mixture if enriched by vapor from petro- 
leum oil so that it burns with a yellow flame, is called water gas and 
is used, alone or with other gases, as illuminating gas. Recall that 
the carbon monoxide makes such a gas poisonous. 

If steam and air are together passed through hot carbon, the gaseous 
product contains nitrogen and some carbon dioxide besides carbon 
monoxide and hydrogen; it is called fuel or producer gas. It is 
easily made and liberates considerable heat in burning, and is there- 
fore used extensively as a fuel in industrial processes, e.g. in mak- 
ing open-hearth steel. 

Carbon monoxide is usually prepared in the laboratory by heating 
a mixture of oxalic acid, or formic acid, and sulphuric acid, and col- 
lecting the gaseous product over water (294) . 

46. Carbon dioxide and monoxide are good examples 
of compounds. — In 9 we learned that compounds have 
three essential characteristics. These are briefly: (i) 
The elements in compounds are united chemically, (2) 
the properties of compounds differ from the elements in 
them, and, most important of all, (3) compounds have a 
definite composition. 



36 PRACTICAL CHEMISTRY 

The chemical conduct, formation, and preparation of 
both oxides show how well these two compounds exhibit 
the first and second characteristics. Both require specific 
chemical action — usually involving heat as an agent 
for their formation, preparation, and chemical conduct. 
And obviously both differ in properties from carbon and 
oxygen, the elements that compose them. 

The third characteristic, viz. constant composition, is not 
apparent from any experiment thus far described. The 
composition of a compound is the proportion by weight of 
each element in it. This proportion can be found by simple 
experiments, though the work must be done accurately. 
One method is to weigh the carbon and oxygen that com- 
bine to form carbon dioxide and also carbon monoxide. 
Another method is to decompose a known weight of each 
compound and weigh the carbon and oxygen obtained. 
We know from many accurate experiments that the propor- 
tion of carbon to oxygen in carbon dioxide is i to 2.66, and 
in carbon monoxide it is i to 1.33. These results mean, to 
repeat, that these two substances are composed of the 
elements carbon and oxygen chemically combined in a 
definite, unvarying proportion by weight. That is, these 
substances are chemical compounds. 

Let us consider these figures more carefully. First, in 
the case of each compound the proportion is definite and 
unvarying. If it were not, these substances would not 
be compounds but mixtures ; in a mixture, you will re- 
member, the proportion of the ingredients may vary (7). 
Second, if we compare the two proportions, we notice they 
are different. If they were not, we should not have the 
two different compounds. Third, if we compare the num- 
bers expressing the oxygen (2.66 and 1.33), we notice a 
simple relation, i.e. one is exactly twice the other. This 



CARBON AND ITS OXIDES 37 

means, in other words, that the weight of the oxygen com- 
bined with the carbon in carbon dioxide is twice the weight 
combined with the carbon in carbon monoxide. 

47. Law of multiple proportions. — There are many other 
cases hke carbon dioxide and carbon monoxide. That is, 
there are groups of compounds of the same elements, and 
in any one group there is a simple multiple relation (1:2, 
2:3, 1:3, etc.) between the weights of the element that 
are combined with a fixed weight of the other element. 
(This is fully worked out in 99.) The general fact of mul- 
tiple relations is sometimes summarized in a brief form called 
the law of multiple proportions, which may be stated 
thus : — 

In a group of compounds of the same elements, small 
whole numbers will express the different weights of one element 
that combine with a fixed weight of the other clement. 

This law and the law of definite composition (9 and 
this section above) are important laws in chemistry. Later 
we shall study them more fully. (See especially Chapter 
VII.) 

EXERCISES 

1. Prepare a brief summary of this Chapter (a) in the form of 
short topics, and {h) as a connected narrative. 

2. Prepare a summary of Chapters I, II, III showing ((/) the re- 
lations of elements and compounds, (/>) the properties of compounds, 
and (f) the laws (4, 9, 47). 

3. In what form does free carbon occur in nature ? Name ten 
familiar solids, three liquids, and two gases which contain carbon. 

4. Name several ways in which carbon dio.xide is formed. 

5. How is carbon dioxide prepared in the laboratory? State the 
properties of carbon dioxide. Describe its chemical conduct. 

6. How is carbon dioxide related to plant and animal life? 

7. Describe a fire extinguisher. 

8. Compare carbon dioxide and carbon monoxide. 

9. How are the two carbon oxides related to a coal fire? 



SS PRACTICAL CHEMISTRY 

10. Describe fully the action of carbon dioxide on calcium hydroxide. 
State the reaction by an equation. 

11. What is the test for (a) carbon, (b) carbon monoxide, (c) car- 
bon dioxide, (d) a carbonate? 

12. State the equation for (a) the oxidation of carbon to carbon mon- 
oxide and (b) the reduction of carbon dioxide to carbon monoxide. 

13. Illuminating gas, water gas, and the gas that escapes from a coal 
fire are poisonous. Why? What is a pulmotor and for what is it 
used? 

14. State and illustrate the law of (c) constant (or definite) com- 
position and (b) multiple proportions. 

15. Define and illustrate reduction. Name two reducing agents 
studied in this chapter. 

16. Make a list of the new chemical words in this chapter and de- 
fine each. 

17. Make a list of the compounds mentioned in this chapter and 
state as fully as possible the elements in each. 

PROBLEMS 

1. What is the weight of lo liters of carbon dioxide gas? Of io,ooo 
cc? Of3l.? 

2. A pupil prepared 5 bottles of carbon dioxide gas each holding 
250 cc. How many gm. of carbon dioxide were prepared? 

3. Marble, if treated with acid, yields about 44 per cent of its weight 
as carbon dioxide. If 0.5 kg. of marble was used, how many (a) gm. and 
(b) 1. of carbon dioxide were formed ? 

4. What weight of marble corresponds to 150 1. of carbon dioxide? 



CHAPTER IV 
HYDROGEN 

48. Occurrence of hydrogen. — Hydrogen, like oxygen, 
is a gaseous element. But it does not occur free to any 
great extent in nature ; natural gas — a mixture of com- 
bustible gases which issues from the earth in certain locaU- 
ties — contains about 2 per cent. Mixtures of gases for 
Hghting and heating, e.g. water gas and producer gas (45), 
contain from 35 to 50 per cent of hydrogen. Combined 
hydrogen is a constituent of many important compounds. 
Water is 11. 18 per cent of hydrogen. The human body is 
about 10 per cent of hydrogen. Hydrogen is a constituent 
of all acids and bases — important classes of compounds 
to be studied later. (See Chapter XII.) 

All plants and animals contain compounds of hydro- 
gen with carbon and oxygen, and in some cases with nitro- 
gen also. 

Compounds of hydrogen and carbon form a large and im- 
portant class of compounds called hydrocarbons, which are 
ingredients of petroleum (and its products, such as kero- 
sene, gasolene, paraffin, and lubricating oils), illuminating 
gas, and producer gas. 

49. Hydrogen is prepared from acids or water. — Hydro- 
gen is readily and conveniently prepared by the interaction 
of certain metals and acids. The metals are usually zinc, 
iron, or magnesium, and the acids are dilute water solu- 
tions of sulphuric acid (H2SO4) or hydrochloric acid (HCl). 
The hydrogen is liberated from the acid, and the metal com- 

39 



40 



PRACTICAL CHEMISTRY 



bines with the rest of the acid to form a compound which 
usually remains dissolved in the liquid. On a large scale 
a Kipp apparatus (Fig. 21) is sometimes used. 

In the laboratory hydrogen is usu- 
ally prepared in a small generator, and 
collected over water in a pneumatic 
trough (Fig. 22). Zinc is put in the 
bottle A and acid is introduced through 
the dropping tube B by pressing the 
clamp. The hydrogen passes out 
through the delivery tube D into the 
pneumatic trough, bubbles up into 
the bottles, and displaces the water. 
No flame should be near during the 
preparation of hydrogen, because mix- 
tures of air and hydrogen explode vio- 
lently when ignited. 

Hydrogen can also be prepared by 
allowing certain metals and water to 
interact. Sodium interacts less rapidly 
than potassium. Calcium interacts 
slowly with water. But potassium 

Q 




Fig. 21. — Kipp ap- 
paratus for generat- 
ing hydrogen 



interacts so rapidly that 
the heat ignites the liber- 
ated hydrogen (Fig. 23). 
If a small piece of sodium 
is dropped upon cold water, 
the sodium melts into a 
shining globule, which spins 
about rapidly on the water 
with a hissing sound and 
finally disappears with a 
slight explosion. If the 




Fig. 22, — Apparatus for preparing 
hydrogen in the laboratory 



HYDROGEN 



41 




Fig. 23. — The interac- 
tion of water and potas- 
sium produces enough 
heat to ignite the liber- 
ated hydrogen 



sodium is wrapped in a piece of fine wire gauze, or 

of tea lead pierced with small holes, and dropped into a 

dish of water, the hydrogen gas can be collected in an 

inverted test tube full of water (Fig. 24). 
Hydrogen, together with oxygen, 

is liberated from water by passing 

a current of electricity through 

water containing sulphuric acid or 

sodium, hydroxide (16, 88). 

Hydrogen can also be prepared 

by passing steam — the gaseous 

form of water — over heated metals 

(Fig. 25). This experiment was 

first performed by Lavoisier, in 

1 783, while he was studying the com- 
position of water. He passed steam 

through a red-hot gun barrel containing bits of iron. 

The oxygen of the steam combined with the iron, and the 
hydrogen escaped from the tube. Since 
Lavoisier was then studying the composi- 
tion of water and not especially the prop- 
erties of hydrogen, he naturally thought 
of the gas as essential for forming water. 
So he named the gas hydrogen, which means 
literally " water former." 

50. Hydrogen can be prepared from alka- 
lies. — Hydrogen can also be prepared by boiling 
solutions of certain alkalies with some elements. 
Thus, if sodium hydroxide (NaOH) is boiled with 
aluminium or silicon, hydrogen is liberated. 

51. A new kind of chemical change 
illustrated by the preparation of hydro- 
gen. — The preparation of hydrogen by 




^ 



Fig. 24. — Appa- 
ratus for collect- 
ing hydrogen 
liberated by the 
interaction of 
water and so- 
dium 



42 



PRACTICAL CHEMISTRY 



the interaction of a metal and an acid, water, or an alkali 
illustrates a third kind of chemical change, viz. substitu- 
tion, or, as it is sometimes called, displacement or replace- 




T^^^ 



Fig. 25. — Modern form of Lavoisier's apparatus for showing the 
formation of hydrogen by the interaction of steam and heated iron 

ment. In the case of zinc and sulphuric acid, zinc is sub- 
stituted chemically for hydrogen, i.e. the hydrogen is dis- 
placed from the acid by the zinc. This chemical change can 
be expressed by the following equation : — 

Zinc -\- Sulphuric /Vcid = Hydrogen + Zinc Sulphate 

(Hydrogen-Sulphur- (Zinc-Sulphur- 

Oxygen) Oxygen) 

Similarly we have : — 

Sodium 4- Water = Hydrogen -|- Sodium Hydroxide 

(Hydro- (Sodium-Hydrogen- 

gen-Oxygen) Oxygen) 

Iron + Water = Hydrogen -\- Iron Oxide 

(Hydro- (Iron-Oxygen) 

gen-Oxygen) 

Aluminium + Sodium Hydroxide = Hydrogen + Sodium Aluminate 

(Sodium-Hydrogen- (Sodium- Aluminium- 

Oxygen) Oxygen) 



HYDROGEN 43 

We define substitution as a chemical change in which 
one element displaces another in a compound. 

52. Some properties of hydrogen. — Hydrogen has no 
taste or color. The pure gas has no odor, though hydrogen 
as ordinarily prepared has a disagreeable odor, due mainly 
to impurities in the metals used. Hydrogen is very slightly 
soluble in water, less so than oxygen. 

Hydrogen is the Ughtest known substance. Volume for 
volume hydrogen is about one fourteenth as heavy as air 
and one sixteenth as heavy as oxygen. One hter at 0° C. 
and 760 mm. weighs only 0.09 gm. (exactly 0.0898 gm.). 
Hydrogen, being so light, diffuses rapidly, i.e. it quickly 
passes through porous substances (e.g. unglazed porcelain, 
rubber, and thin sheets of metal), mixes rapidly with other 
gases, and freely escapes into space in all directions. 

The extreme lightness as well as the rapid diffusion of hydrogen 
can be shown by simple experiments. If a bottle of hydrogen is ex- 
posed to the air a minute or two, and a lighted match then dropped 
in, the match merely burns ; if hydrogen were present, a loud explo- 
sion would have occurred. Or, if a bottle of hydrogen is held just 
beneath a bottle of air, the gases quickly change places more or less 
completely, the hydrogen rising into the upper bottle and forcing 
out some of the air ; if the experiment is well done, the gas in the upper 
bottle burns or explodes gently, but usually the loud explosion shows 
that only a part of the hydrogen flowed into the upper bottle. 

53. Chemical conduct of hydrogen. — At ordinary tem- 
peratures and under ordinary conditions, hydrogen, like 
oxygen, is not an active element. A mixture of hydrogen 
and oxygen can be kept indefinitely at the temperature 
of the laboratory. But if the mixture is heated to about 
800° C. or if a flame is brought very near it, the gases unite 
with a violent explosion. 

Under special conditions hydrogen unites with oxygen 
quietly, i.e. hydrogen can be made to burn quietly in oxygen 



44 



PRACTICAL CHEMISTRY 




or air. Hydrogen is generated in the apparatus shown in 
Fig. 26 ; the gas passes through the drying tube and escapes 
in a fine stream through the small opening in the platinum 
tip. After all the air has been driven out of the whole 

apparatus by the hydro- 
gen, the gas is Hghted by 
holding a lighted match at 
the end of the tip. The 
hydrogen burns in the air 
with an almost invisible 
but very hot flame. If 
a small, dry, cold bottle 
is held over the flame, 
26. — Apparatus for burning water vapor is deposited 
hydrogen inside the bottle. Water 

is the product of the combustion of hydrogen. That is, 
hydrogen in burning unites with oxygen, just as other 
burning substances do. Thus : 

Hydrogen -f Oxygen = Water 
This chemical change is an example of combination and 
also of oxidation (22). The two elements, hydrogen and 
oxygen, unite to form the compound water ; hydrogen is 
oxidized, and the product might be called hydrogen oxide, 
though it is called by its more familiar name water. 

The film of water that may be seen on the bottom of a vessel placed 
over a lighted gas range or a Bunsen burner is the condensed vapor 
formed by the burning hydrogen, and hydrogen compounds, of the 
illuminating gas. Organic substances containing hydrogen, such as 
wood and paper, when burned, yield water as one of their products. 

Although a small jet of hydrogen burns quietly in air or 
in oxygen, a mixture of hydrogen and air burns so rapidly 
that the combustion is practically an explosion. There- 
fore, the air should be fully expelled from the apparatus 



HYDROGEN 45 

in which hydrogen is being generated and all leaky joints 
should be tightened before the gas is collected ; no flames, 
large or small, should be near. Neglect of these precau- 
tions has caused serious accidents. 

The chemical conduct of hydrogen with the element chlorine is 
similar to that with oxygen. If the two gases are mixed in the dark, 
they do not react. But if a mixture of hydrogen and chlorine is 
heated or exposed to the sunlight, the two gases combine with ex- 
plosive violence. However, a hydrogen flame, if lowered into a 
bottle of chlorine, continues to burn quietly. In this case, as with 
oxygen, the two elements, hydrogen and chlorine, unite ; the product 
is the compound hydrogen chloride. The burning of hydrogen in 
chlorine illustrates an extension of the term combustion. No oxygen 
is involved, but it is a case of chemical combination accompanied 
by light and heat. (See 25.) 

Certain metals under special conditions hasten the rate 
at which hydrogen combines with elements. Thus, if a 
mixture of hydrogen and oxygen is passed over finely di- 
vided platinum, the gases, which ordinarily would scarcely 
combine at all, now begin to react to form water. Similarly, 
hydrogen and nitrogen can be made to unite into the com- 
pound ammonia, if the mixture is passed under proper 
conditions over certain metals. The platinum and the 
other metals, as far as we know now, do not undergo a 
chemical change in these reactions. They hasten a very 
slow chemical reaction. A metal w^hich acts thus is called 
a catalyst or a catalytic agent. Its function is sometimes 
compared to that of lubricating oil on a machine. 

54. Hydrogen does not support combustion. — Hydro- 
gen burns, but does not support combustion. These facts 
are illustrated by putting a hghted taper into an inverted 
bottle of hydrogen (Fig. 27). The taper ignites the 
hydrogen, which burns at the mouth of the bottle. The 
taper does not burn inside the bottle, whereas when it 



i 



PRACTICAL CHEMISTRY 

is slowly withdrawn through the burning hydrogen it is 
relighted. 

55. Hydrogen is a reducing agent. — Hydrogen not 
only combines energetically with free oxygen, but it also 

^ ^ withdraws oxygen from compounds. This 

chemical removal of oxygen is called re- 
duction, and the substances that remove 
the oxygen are called reducing agents. 
(Compare 43.) Hydrogen is a vigorous 
reducing agent, just as oxygen is an ener- 
getic oxidizing agent. When oxides of 
^T , certain metals are heated in a current 

Fig. 27. — Hydro- 
gen burns but of hydrogen, the oxygen of the oxide is 

does not support chemically removed and combines with the 
combustion hydrogen^ to form water; the metal is 

left uncombined. Thus, by heating copper oxide in hydro- 
gen, water and metalHc copper are produced. Chemically 
speaking, the copper oxide is reduced by the hydrogen. 
The chemical change is substitution (the hydrogen being 
substituted chemically for the metal), and it can be ex- 
pressed thus : — 

Copper Oxide + Hydrogen = Water + Copper 

(Copper-Oxygen) (Hydrogen-Oxygen) 

This chemical change can be interpreted from the 
standpoint of oxidation, because the hydrogen is oxidized 
to water at the same time the copper oxide is reduced. 
In fact, the processes of reduction and oxidation are closely 
related and either one may be emphasized in interpreting 
the chemical change. In its simplest form, reduction is 
the opposite of oxidation. Later we shall see that the terms 
oxidation and reduction are both used in a broader sense. 

56. Test for hydrogen. — A simple test for hydrogen is that it 
extinguishes a small flame, such as a blazing taper or joss stick, but 



HYDROGEN 47 

is lighted at the same time, often with an explosion, and continues to 
burn until the gas is exhausted. A conclusive test is that it burns 
with a hot flame and forms water as the sole product. 




Fig. 28. — Welding an iron grill with an oxy-acetylene flame 

57. Uses of hydrogen. — On account of its extreme light- 
ness, hydrogen is used to fill balloons and dirigible airships ; 
small balloons are usually filled with coal gas and larger 
dirigible craft will, it is predicted, be filled with the in- 
combustible gas helium (127). 

The intense heat of the hydrogen flame is utilized in the 
oxy-hydrogen blowi^ipe. The essential part of the burner 
is two pointed metal tubes. The inner and smaller one 
is for oxygen, and the outer and larger one for hydrogen; 
the gases are forced out of these small openings by the pres- 
sure maintained in the storage tanks. The temperature 
of the oxy-hydrogen flame is about 2000° C. The flame is 
used to melt platinum. When the flame strikes against a 
piece of lime, the latter becomes intensely bright. Thus 
used, it is called the hme or calcium Hght, and is utihzed 
in the stereopticon. The oxy-hydrogen flame has been 
largely replaced by the electric furnace and the oxy-acety- 



48 



PRACTICAL CHEMISTRY 




Fig. 29. — A blast lamp 



lene flame (Fig. 28) as sources of intense heat. (Acetylene 
is a compound of carbon and hydrogen — C2H2.) 

A substitute for the oxy-hydrogen flame is used in 

the laboratory. It is 
called a blast lamp 
(Fig. 29). Illumi- 
nating gas (which 
contains hydrogen 
and hydrocarbons) 
and air are used in- 
stead of hydrogen 
and oxygen. 

The most extensive 
use of hydrogen is in 
transforming certain oils, e.g. cotton-seed oil, into sohd edible fats. 
This process is called hydrogenation (363). 

The hydrogen needed for these uses is prepared by the 
electrolysis of water (16). 

EXERCISES 

1. Prepare a summary of this chapter. 

2. Compare oxygen and hydrogen in tabular form. 

3. How can hydrogen be distinguished from (a) oxygen, (b) car- 
bon monoxide, (c) carbon dioxide, (d) air? 

4. Summarize the conspicuous properties of hydrogen. Describe 
its chemical conduct. 

5. Why is there danger of an explosion in generating hydrogen? 
How can the danger be avoided? 

6. Define and illustrate (a) reduction and (b) reducing agent. Com- 
pare with (a) oxidation and {b) oxidizing agent. 

7. Make a list of the new chemical words in this chapter and de- 
fine each. 

8. In using hydrogen for balloons, what property of the gas might 
cause disaster? 

9. Topics for home study, (a) Burning of hydrogen, (b) Re- 
lation of hydrogen to water, (c) Lavoisier's experiment, [d) Re- 
view of chemical change, (e) Uses of hydrogen. 



HYDROGEN 49 

PROBLEMS 

1. Sulphuric acid contains 2.04 per cent of hydrogen, (a) How 
many grams must be decomposed to yield 85 gm. of hydrogen (at 0° C. 
and 760 mm.)? (b) 85 cc? 

2. Hydrochloric acid contains 2.74 per cent of hydrogen. How 
many tons must be decomposed to yield a ton of hydrogen? 

3. Water contains 11. 18 per cent of hydrogen. How many grams 
of hydrogen can "be prepared from 230 gm. of water? How many 
liters (at 0° C. and 760 mm.) ? 

4. (a) How many liters (at 0° C. and 760 mm.) will 45 gm. of hydro- 
gen occupy? (b) How many grams will 45 1. weigh? 

• 5. A student prepared enough hydrogen (at 0° C. and 760 mm.) 
to fill six bottles, each holding 250 cc. (a) How many grams were 
prepared? (b) How much sulphuric acid was used up? 

6. A cylindrical tank i m. long and 25 cm. in diameter is filled with 
hydrogen (at 0° C. and 760 mm.). How many grams does the gas 
weigh ? 

7. A hydrogen manufactory produces daily 19,000 cubic meters of 
gas. (a) Express this volume in liters and in cc. (b) What would 
this volume weigh, if measured at 0° C. and 760 mm.? 

8. A Zeppelin balloon had a capacity of 351,150 cubic feet. What 
weight of hydrogen was needed to fill it? (Assume i cu. m. = 35.32 
cu. ft. ; also that the volume of hydrogen was measured at 0° C. and 
760 mm.) 



CHAPTER V 
THE MEASUREMENT OF GASES 

58. Introduction. — So far we have studied four gases : 
the two elements, oxygen and hydrogen, and the two com- 
pounds, carbon dioxide and carbon monoxide. We shall 
study many other gases in the succeeding chapters. 

59. What is our problem? — In chemistry we often need 
to know the weight of a given volume of gas, or to compare 
the weights of the same volume. But we cannot deter- 
mine the weight of a gas nor compare weights until we agree 
on the conditions under which we are to measure the vol- 
ume. Thus, when we say one hter of oxygen wxighs 1.43 
gm., we really mean that the hter has this weight if the vol- 
ume is measured at a certain temperature and pressure 
(0° C. and j6o mm.). 

All gases change in volume with changes in tempera- 
ture and pressure. In this chapter we shall study: (i) 
the effect of changes of tem.perature and pressure on 
the volume of a gas, (2) how the required volume of a 
gas is found at the standard temperature and pressure, 
and (3) how the weight of a given volume of a gas is found. 

60. Change in the volume of a gas with changes in tem- 
perature. — Gases expand when heated and contract when 
cooled. This change in volume is uniform for all gases, pro- 
vided of course there is no change in pressure. Thus, if 
the pressure is kept constant, 273 cc. of a gas at 0° C. be- 
comes 274 cc. at 1° C, 280 cc. at 7° C, 272 cc. at -1° C, 
266 cc. at -7° C, and so on. That is, for each degree of 

so 



THE MEASUREMENT OF GASES 



51 



CENTIGRADE AliSOLUTE 
Water 



100^ 



O'' 



•182.5^ 



Boils 



Water 



Freezes 



Oxytren 



Boils 



Absolute 



3730 



273° 



change in temperature the volume at o"^ C. changes ar^- 
This general fact is stated as the law of Charles, thus : — 

Gases under constant pressure change in volume uniformly 
with the same change in temperature. 

At this rate of contraction a gas would have no vol- 
ume at —273° C.I But this rather startUng result does 
not actually happen, because gases 
become liquids above this temperature. 
Nevertheless this point(— 273°) on the 
centigrade thermometer is useful, for 
it serves as the starting point of a 
temperature scale called absolute tem- 
perature. The temperature — 273° C. 
is called absolute zero, and tempera- 
tures reckoned from this point as zero 
are called absolute temperatures. If 
an "absolute thermometer" were 
constructed, and compared wdth a cen- 
tigrade thermometer, the scales would 
be seen to be simply related (Fig. 30). 
If we designate absolute temperatures 
by A. and centigrade by C, then we 
see that 273° A. is 0° C, 373° A. is 
100° C, and 0° A. is —273° C. That 
is, absolute degrees are obtained by 
adding 273 to centigrade degrees. 

How is absolute temperature used ? 
Suppose, as above, we have 273 cc. of gas at 0° C. This 
volume becomes 274 cc. at 1° C. and 280 cc. at 7° C. Now 
0° C, 1° C, and f C. are 273° A., 274° A., and 280° A. 
That is, stated in general terms, the volumes of a given 
weight of gas at different temperatures are in the same 
ratio as the absolute temperatures. 



90.5° 



Ze; 



0° 



Fig. 30. — Centigrade 
and absolute scales 



52 PRACTICAL CHEMISTRY 

61. How we apply the law of Charles. — Suppose we 
have lOO cc. of oxygen at 25° C. and we wish to know 
what the volume would be at 0° C. It is not necessary 
to cool the gas to 0° C. and measure the volume. We know : 
(i) that a gas contracts uniformly for each degree of de- 
crease in temperature, and (2) that the volumes are in the 
same ratio as the absolute temperatures. Hence we can 
compute the volume to which the 100 cc. would contract 
if it were cooled from 25° to 0° C. The steps in the pro- 
cess are these : {a) change the centigrade temperatures 
to absolute temperatures by adding 273 to each; (b) make 
273 (i.e. o -f 273) the numerator of a fraction and the other 
sum the denominator ; (c) multiply the volume by this 
fraction. Thus: (a) o + 273 = 273, and 25 + 273 = 298; 
(b) Hi; (c) 100 X Ui = 91.61. That is, 91.61 cc. is the 
volume 100 cc. would become if cooled from 25° C. to o^ C. 

In solving problems involving change in temperature, care should 
be taken to notice the conditions. For example, 273 is the numerator 
only when the final temperature is 0° C. ; if the final temperature is 
another number, the numerator is this number + 273. In checking 
results, it should be remembered that decrease in temperature 
means decrease in volume. 

62. Change in the volume of a gas with changes in pres- 
sure. — Many gases are collected in bottles or tubes over 
water or mercury in a pneumatic trough or tall jar. In 
measuring the volume of the gas, the levels of the liquid are 
made the same inside and outside the bottle or tube by 
raising or lowering it. The gas thus becomes under at- 
mospheric pressure, i.e. the pressure of the atmosphere 
exerted on the exposed surface of the liquid in the trough 
or jar is transmitted through the water to the gas. Hence 
the pressure which the gas is under is the same as the pres- 
sure of the atmosphere when the gas volume is read. 



THE MEASUREMENT OF GASES 



53 



■SOO 



7.-;^) 



700 



The pressure of the atmosphere is found merely by read- 
ing the barometer. A common form of barometer is shown 
in Fig. 31. It consists of a small-bore, strong 
glass tube, about one meter long, and closed 
at the upper end. The tube is nearly full of 
mercury and the open, lower end dips into a 
small reservoir of mercur>\ The space above 
the mercury at the upper end of the tube is 
a vacuum. As the pressure of the atmosphere 
changes, the column rises or falls. Near the 
top of the supporting board back of the tube 
is a scale by which we can tell the height of the 
mercury column above the surface of the mer- 
cury in the reservoir. That is, by reading on 
the scale the height of the mercury; — '' reading 
the barometer " — we are measuring the pres- 
sure of the atmosphere at the time of the ob- 
servation. The normal, or average, height of 
the barometer is 760 millimeters (mm.). 

As stated in 59 the volume of a gas changes 
with change in pressure. The volume con- 
tracts if the pressure is increased and expands 
if the pressure is decreased. The effect of pres- 
sure on the volume of a gas was first studied by 
Boyle (Fig. 32). Fie found that 100 cc. of air, 
for example, contracts to 50 cc. if the pressure 
is doubled, and also that 100 cc. expands to 
200 cc. if the pressure is halved. This relation of volume 
to pressure, which applies to all gases, is sometimes stated 
as the law of Boyle, thus : — 

The volume of a gas at constant temperature changes in- 
versely with changes in pressure. 

63. How we apply Boyle's law. — In most of the experi- 



Fig. 3I--A 
barometer 



54 



PRACTICAL CHEMISTRY 



ments in chemistry we actually read a gas volume at the 
prevailing pressure, although we need to know what the 
volume would be if the pressure were 760 mm. As in the 

case of temperature and 
volume, it is not neces- 
sary (and certainly not 
convenient !) to wait 
until the barometer be- 
comes 760 mm. We 
know that volumes are 
inversely related to their 
corresponding pressures 
(62) . Hence we can com- 
pute the volume which 
100 cc. of gas, for ex- 
ample, would have if the 
pressure were changed 
from 775 mm. to 760 
mm. The steps in the 
process are these : {a) Make 760 the denominator of a frac- 
tion and 775 its numerator; (b) multiply the volume by 
this fraction. Thus: (a) -fjf ; (b) 100 X fe-l" = 101.97. 




Fig. 32. — Boyle (1626-1691 



In solving problems involving change in pressure, care should be 
taken to notice the conditions. (Compare end of 61.) For example, 
760 is the denominator of the fraction only when the final pressure is 
the normal pressure (760 mm.) ; if the final (or desired) pressure is 
another number, the denominator is this number. It is advisable 
also to check the result by comparison with the original volume, 
remembering that decrease in pressure means increase in volume. 

64. How we reduce a gas volume to standard conditions. 

— Measuring gases usually involves reading both tempera- 
ture and pressure. The normal or standard temperature 
selected in chemistry for measuring gases is 0° C, and the 



THE MEASUREMENT OF GASES 



55 



normal or standard pressure is 760 mm. These conditions 
(o° C. and 760 mm.) are called normal or standard con- 
ditions. It is inconvenient, often impossible, to measure 
gas volumes at exactly 0° C. and 760 mm. So it is cus- 
tomary to measure the volume at the prevailing tempera- 
ture and pressure, and then compute the volume the gas 
would have if it were at 0° C. and 760 mm. This mathe- 
matical calculation is called reducing to standard conditions 
or correcting the volume for temperature and pressure. 
The final volume is called the corrected volume. Let us 
take an example. Suppose a gas volume measures 100 cc. 
at 25° C. and 775 mm., and we wish to reduce this observed 
volume to standard conditions. We apply the laws of 
Charles and Boyle, and merely combine the two mathe- 
matical processes already described (61, 63). Thus : ■— 



lOO A T98" X Te^o^ 



9341 




Fig. 7,7,. — Apparatus for finding the weight of a liter of oxygen 



65. How we find the weight of a given volume of a gas. — 
In preceding sections the weight of one liter of different 
gases is given. Thus, oxygen is 1.43, carbon dioxide 
is 1.98, carbon monoxide is 1.25, and hydrogen is 0.09 gm. 



56 PRACTICAL CHEMISTRY 

Let us see how the weight of one Uter of oxygen is 
found, (a) The apparatus is shown in Fig. 33. A mix- 
ture of potassium chlorate and manganese dioxide is put 
in the test tube A. The part AF is weighed. The bottle 
B is filled with water. The empty bottle D is weighed. 
The mixture is heated and oxygen forces water from B 
into D. When sufficient gas has been liberated, the heat- 
ing is stopped and the apparatus is allowed to cool. 
(b) The temperature and pressure are read — say 20° C. and 
755 mm. The levels in B and D are made the same (by 
raising one bottle). The water in D is measured ; its vol- 
ume is the same as the volume of the oxygen — say 1.75 liters. 
AF is weighed ; its loss is the weight of the oxygen — say 
2.322 gm. (c) The observed volume is reduced to stand- 
ard conditions; thus: 1.75 X ffl X fro = 1-625. (d) 
The weight of one Uter of oxygen at 0° C. and 760 mm. is 
found by dividing the weight of the oxygen by its corrected 
volume; thus, 2.322 -7- 1.625 = 1.429. 

We shall see later that a slight modification must be made in the 
value of the pressure when the oxygen is collected over water (74). 

66. The nature of gases. — We have seen in this chapter 
that gases change uniformly in volume with changes in 
temperature and pressure. They behave alike in many 
other ways, e.g. they diffuse readily. The similarity in 
properties suggested long ago that gases are fundamentally 
alike. We beheve that gases are made up of minute parti- 
cles, too small to be seen with a microscope. These parti- 
cles are called molecules. The molecules of a gas are far 
apart, i.e. the distances between molecules are large com- 
pared with the molecules. They are exceedingly small 
particles in a large space. Furthermore, we believe that 
the molecules are in constant motion, i.e. flying about 



THE IMEASUREMENT OF GASES 57 

rapidly in all directions, striking each other and the walls 
of the containing vessel, rebounding, and so on ceaselessly. 
Moreover, the movements, so it is believed, increase in 
velocity as temperature rises, and decrease as it falls. 

These suppositions are part of the kinetic-molecular 
theory of gases. We cannot see the moving (kinetic) mole- 
cules, but many facts lead us to beheve in their existence. 
We state our belief as a theory, i.e. a supposition or mental 
picture which enables us to interpret related facts. 

The law of Boyle seems much clearer if we interpret 
it by the kinetic-molecular theory. Thus, when a gas is 
compressed, the molecules are pressed more closely to- 
gether. And when a gas is compressed to half its volume, 
the pressure produced by the blows of the moving mole- 
cules is doubled because the number of blows per second 
against the walls is doubled. 

Similarly, the law of Charles is more readily understood 
if we think of the m.olecules of a gas as moving more 
rapidly, and consequently requiring more space when the 
temperature is raised. 

Again, the constant m^otion of the molecules helps us 
understand the rapid movement of gases called diffusion, 
e.g. the rising of illuminating gas throughout a building 
from a small leak in the cellar. 

More will be said later about the nature of gases ; the nature of 
liquids, too, will be considered. (See 86 and 101.) 

EXERCISES 

1. Prepare a summary of this chapter. 

2. (a) State Boyle's law. Illustrate it. (b) State Charles's law. 
Illustrate it. 

3. Give examples from everyday life of {a) expansion and of (b) con- 
traction of gases caused by change of temperature. 

4. Apply E.xercise 3 to change of pressure. 



58 PRACTICAL CHEMISTRY 

5. (c) Change these centigrade readings to absolute : loo, o, 
IS) ~i5) 250, 273, —273. (b) Change these absolute readings to 
centigrade: 273, o, 200, 100, 473, 180, 373. 

6. (a) When a given volume of gas is reduced to standard con- 
ditions, is the weight of the gas changed? (b) Is the gas itself actually 
reduced to 0° C. and 760 mm.? 

7. From the data given in 65, calculate the weight of a liter of 
oxygen without making the correction for temperature and pressure. 
Compare the result with the correct weight. 

8. Topics for home study, (a) Boyle's contributions to science. 
(b) Thermometers, (c) Barometers, (d) Atmospheric pressure. 

PROBLEMS 

1. Reduce the following to the volume occupied at 760 mm. : 
(a) 20 cc. at 745 mm. ; (b) 45 cc. at 765 mm. ; (c) 450 cc. at 755 mm. ; 
(d) 1.5 1. at 763 mm.; (e) 2.5 1. at 745 mm.; (/) 500 cc. at 75 cm.; 
(g) 76 cc. at 76 cm. ; (h) 900 1. at 749 mm. 

2. Reduce the following to the volume occupied at 0° C. : (a) 170 
cc.at8o°C.; (b) 450 cc. at 15° C. ; (c) 70.6 cc. at 17° C. ; (d) 49 cc. 
at 19° C. ; (e) 356 cc. at 34° C. ; (/) 48 cc. at 27° C. 

3. Reduce the following to the volume at standard conditions : 
(a) 250 cc. at 780 mm. and 20° C. ; (b) 140 cc. at 745 mm. and 21° C. 

4. Reduce the following to the volume at standard conditions : 
(a) 247 cc. at 720 mm. and 14° C. ; (b) 1000 cc. at 750 mm. and 18° 
C. ; (c) 1480 cc. at 765 mm. and 81° C. 

5. A volume of oxygen measured 375 cc. when the barometer was 
740 mm., and the thermometer was 27° C. What would be the volume 
at the standard pressure and temperature? Ans. 332.3 cc. 

6. Find the weight of 29 cc. of oxygen at 23° C. and 776 mm. 
Ans. 0.039 gm. 

7. Calculate the weight of hydrogen in a vessel of 10 liters capacity, 
filled when the barometer reads 756 mm. and the thermometer 18° C. 

8. If a volume of hydrogen measures 100 cc. at 14° C. and 755 mm., 
what will be its volume when measured at —8° C. and 780 mm.? 

9. A gas measures 637 cc. at 755 mm. and 17° C. Find its volume 
at 730 mm. and 30° C. 

10. Correct 250 cc. of oxygen at 18° C. and 745 mm. for tem- 
perature and pressure. Ans. 229.9 cc. 

11. (a) What is the volume of 200 gm. of hydrogen at 0° C. and 
760 mm.? (b) What would be its volume at 15° C. and 750 mm.? 



CHAPTER VI 
WATER 

67. Importance and occurrence of water. — Water is 
one of the most familiar of natural substances. Its varied 
properties and common uses make it an indispensable sub- 
stance. It is a compound of hydrogen and oxygen. 

Water is always present in the air as a vapor, which is 
continually condensing into rain, clouds, mist, fog, dew, 
hail, frost, and snow. W^ater occurs in vast quantities on 
and beneath the surface of the earth as a liquid ; and also 
as a solid (snow and ice). The soil and plants contain con- 
siderable water. Many common foods, especially vege- 
tables, contain from 40 to 90 per cent of water. The human 
body is nearly 70 per cent water. 

68. Natural waters are not pure. — Water is never found 
pure in nature. Even rain water, which is usually regarded 
as the purest natural water, contains dust and gases washed 
from the air. Water which flows along the surface of the 
earth or underground dissolves substances from the rocks 
and soil. Hence river water contains earthy impurities 
brought by the underground and surface water ; it is also 
often contaminated with compounds formed by the decom- 
position of animal and vegetable matter, the so-called ''or- 
ganic matter," or with refuse from manufactories. 

Ocean water contains a large proportion of impurities, 
especially mineral substances Hke common salt and similar 
compounds of calcium and magnesium. The peculiar taste of 
ocean water is due chiefly to the presence of these substances. 

69. Purification of water. — Since natural waters are not 
pure, it is often necessary to remove certain impurities to 

59 



6o 



PRACTICAL CHEMISTRY 



make the water suitable for the desired use. Besides dis- 
solved mineral matter and organic matter, water may con- 
tain suspended matter such as fine particles of clay or other 
earthy substances and partly disintegrated organic sub- 
stances. Water, too, often contains sewage or organic 
matter and bacteria more or less associated with sewage. 
Water used for drinking and cooking should be as pure 
as possible, and it is desirable as well as economical that 
water be purified sufficiently for all practical purposes. The 
water of some towns and cities is purified by filtering it 
slowly on a large scale through layers of sand and gravel. 
Such a filter remioves suspended matter almost completely, 
though it must be frequently cleaned. In some locaUties 
the water is stored in a large settling basin or reservoir ; 
here the suspended soHd matter slowly settles, the process 
sometimes being hastened or aided by adding alum, which 
forms a sticky substance to which particles cling. Some- 
times the water is freed from organic matter by spraying 
it into the air (Fig. 34). This is an oxidation process. 




Fig. 34. — Purification of water by spraying it into the air. An 
aerator of the New York City water system by which 376 million 
gallons are purified daily 



WATER 



6i 



The most effective method of destroying organic matter, 
especially bacteria, is by chemical treatment. Ozone, a 
gas like oxygen but much more active, is sometimes used 
(30). In recent years chlorine, or one of its compounds, 
has come into general use because of its simplicity and 
certainty. A small amount of liquid chlorine is allowed to 
flow into the entering supply (Fig. 35). During the war, 




Fig. 35. — Plant for the purification of water by chlorine. A chlorinator 
of the New A'ork City water system by which 400 million gallons are 
purified daily. 

water contaminated through accident or intent was often 
rendered fit for drinking by means of chlorine compounds. 

Water containing bacteria can be purified on a small scale or in 
an emergency, e.g. for household use during an epidemic, by boiling 
ten or fifteen minutes, and then putting it in a bottle or jar stoppered 
with cotton. The bottle or jar for keeping the water should also be 
boiled in water before use 

If the purity of a drinking water is doubtful, a sample should be 
subjected to a chemical and microscopic examination, supplemented 
by a rigid sanitary inspection of the surroundings and the source of 
supply. 



62 



PRACTICAL CHEMISTRY 



70. Distillation. — Water can be purified on a small or 
local scale by distillation. This operation is often per- 
formed in the laboratory in a condenser, which is shown in 
Fig. 36 arranged for use. 




Fig. 36. — Condenser arranged for distillation of water. 

The condenser consists of an outer tube AA', provided with an 
inlet and an outlet for a current of cold water which surrounds the 
inner tube BB'. The vapor from the w^ater 
boiling in the flask C condenses in the inner 
tube, owing to the decrease in temperature, 
and drops off the lower end of this tube, as 
the distillate, into the receiver D, while the 
non-volatile impurities remain behind in the 
flask. Other forms of condensers are used, 
especially for continuous work (Fig. 37). 
Cold water enters the condenser at the lower 
inlet and is kept level in the chamber by the 
upper outlet. The chamber is heated, and 
th-e steam in passing down through the con- 
denser drops off the lower end as distilled 
water. 

Distilled water is prepared on a large scale 

by boiling the water in a metal vessel and 

condensing the vapor in a block tin pipe 

coiled around the inside of a vessel through which a current of cold 

water is flowing (Fig. 38). 




Fig. 37. — Apparatus 
for distilling water 



WATER 



6,3 




Fig. 38. — Coiled pipe 
condenser 



Distilled water has a Hat taste. If it is to be used as a beverage, 
air is bubbled through the water, which soon acquires the accustomed 
flavor. i\Iuch distilled water is used in the chemical laboratory to 
prepare solutions and in experiments requiring water free from 
organic and mineral matter. 

71. Some properties of water. — At ordinary temper- 
atures pure water is a tasteless and odorless liquid. It 
is usually colorless, but thick layers 
are blue. When water is cooled suffi- 
ciently, the liquid becomes the familiar 
soKd, ice. The temperature at which 
water solidifies or freezes is 0° C. (or 
32° F. — Fahrenheit). When water 
freezes, it expands about one tenth of 
its volume. That is, a given volume 
of water produces a larger volume of 
ice. If we weigh the same volume of 
water and ice, we find the ice weighs less. In other words, 
the specific gravity of ice is less than i, which is the 
standard. Since the specific gravity of ice is about 0.92, 
ice floats in water. 

The pressure exerted by water when it freezes is powerful. 
Vessels 01 pipes completely filled with water often burst when the 
water freezes. It is a popular idea that " thawing out " a pipe bursts 
it. This is not true, because ice contracts when it melts. As a 
matter of fact, pipes crack as soon as the water freezes, and when the 
ice melts, the water flows out of the crack. 

Ice melts at 0° C. (32° F.), which is also the freezing point 
of water. Ice often crystallizes in forming, but individual 
crystals are seldom visible except during the first stages of 
the process. Snow crystals are common (Fig. 30). They 
are always six-sided or six-pointed, and are formed in the 
atmosphere by the freezing of water vapor. 



64 



PRACTICAL CHEMISTRY 




When water is heated sufhciently in an open vessel, the 
liquid becomes a vapor, and the vapor escapes rapidly 

^ until the temperature 
reaches ioo° C. (or 212° 
F.). At this point 
water boils, i.e. it 
changes rapidly into 
vapor without rise of 

temperature. This 
Fig. 39. — Snow crystals. (From a photo- . . . 

graph by permission of Wilson A. Bentley) vapor IS mviSlble, but 

as it leaves the vessel 
it cools and condenses quickly into a cloud of minute 
drops of liquid water. This cloud is called steam. 

The relation of water vapor to steam can be shown by a simple 
experiment. Water is put in a flask (Fig. 40) and boiled vigorously. 
The flask is now full of invisible water vapor and steam is seen es- 
caping from the bent exit tube. When the steam itself is heated, the 
cloud disappears from the end of 
the exit tube, i.e. the vapor no 
longer condenses into droplets 
but escapes unchanged as an in- 
visible gas. 

Water exists in three states 
— liquid, soHd, and gaseous. 
That is, water, ice, and 
vapor are three common 
states of the same compound. 
And, furthermore, the trans- 
formation from one state to 
another is a matter of tem- 
perature. Hence the tem- 
peratures at which these ^.^ ^^ _ Experiment to show the 
transformations take place relation of water vapor to steam 




WATER 65 

arc important; they should be learned. Change of state 
does not lead to the formation of a new compound. Such 
a change is called a physical change. 

72. Evaporation. — Licjuid water is always changing 
into vapor, whatever the temperature. This process is 
called evaporation. Water vapor is escaping constantly 
on an enormous scale from the surface of the ocean, lakes, 
and rivers. This vapor is transported by air currents to 
great heights and to regions remote from the water surface. 
When the vapor reaches places where the temperature is 
low, a part condenses to the liquid or solid state and pro- 
duces . clouds, rain, snow, or other forms of water. By 
evaporation heat is absorbed. By condensation heat is lib- 
erated. These two processes produce a fundamental effect 
on climate, not only in regulating temperature but in dis- 
tributing water through the air and upon the land. 

On a small scale water vapor is escaping from puddles of water, 
moist soil, and wet objects. We speak of this process as drying. 
The rate at which drying takes place depends largely on the amount 
of water vapor in the air, the rate being in general low on wet days and 
high on dry days. This subject will be treated in Chapter IX. 

73. What is vapor pressure ? — Evaporation produces 
pressure. This fact is not apparent in the mere escape of 
water vapor into the air from a surface of water or from 
a wet object. Nevertheless the pressure is produced and 
it is called the vapor pressure of water, or vapor pressure. 

A simple experiment will illustrate the fact of vapor pressure. 
The apparatus is shown in Fig. 41. The dry bottle (left) is fitted 
with an open U-shaped tube partly filled with a colored liquid {e.g. 
ink) to serve as an indicator of pressure. When the stopper is re- 
moved, a littlj water poured into the bottle, and the stopper quickly 
replaced, the water begins to evaporate. As the water evaporates, 
the colored liquid shows an increase in pressure (right). 



66 



PRACTICAL CHEMISTRY 



The pressure exerted by water vapor depends solely on 
the temperature. This is readily seen by comparing the 



n 






^£\ 



u 



u 



' Fig. 41. — Experiment to illustrate vapor pressure 

heights of the mercury in the fine-bore tubes shown in 
Fig. 42. Each tube was first filled with mercury and in- 
verted in the dish of mercury. In each tube 
the mercury sank to the same point (760). 
In tube A there is no water vapor in the 
space above the mercury, and the height of 
the mercury column is 760 mm. A small 
drop of water is forced up into the tubes 
B and C by means of a medicine dropper. 
In B the space above the mercury is filled 
with water vapor at 20° C. ; the vapor 
exerts a pressure and forces the mercury 
(^ UK,^ down to nearly 742 mm. That is, water 
\ / vapor at 20° C. exerts a pressure equal to 

18 mm. of mercury. Similarly, in C the 

'per^ment to' ^pace is filled with water vapor at 50° C, 
show the rela- and the mercury is forced down to 668 mm., 
tion between ^]^g water vapor at this temperature ex- 
vapor pressure , . r 
•and tempera- "ting a pressure of 92 mm. 
ture If the water vapor in a tube were at loo 



WATER 67 

C, the vapor pressure would be 760 mm. The latter value 
is instructive, for it means that at the boiling point of water 
(100° C.) the vapor pressure equals numerically the nor- 
mal atmospheric pressure. This means in other words that 
the vapor escaping from water boiUng in an open vessel 
overcomes the pressure of the atmosphere upon the surface 
of the water. Since the normal pressure of the atmos- 
phere is 760 mm., the normal boiling point, so to speak, 
is 100° C. 

The boiling point becomes lower as the pressure is decreased and 
higher as the pressure is increased. Warm water will boil under the 
receiver of an air pump and on the top of a high mountain. In a 
pressure cooker the temperature of the water is above 100° C. 
In a vacuum vessel, such as is used to evaporate sugar solutions, the 
boiling point is often as low as 70° C. 

The pressure exerted by water vapor depends solely, 
as shown above, on the temperature of the evaporating 
water, and has a maximum value for each temperature. 
These values have been carefully determined by experi- 
ment, and can be found in the Table of Vapor Pressure 
given in the Appendix, § 4. 

74. A practical application of vapor pressure is made in finding 
accurately the weight of a Uter of oxygen and in similar experiments 
where gases are measured over water. The oxygen is collected 
in a bottle or graduated tube inverted in a vessel of water. The gas 
should be allowed to stand confined over the water long enough to 
become saturated with water vapor, i.e. the tube finally contains 
a mixture of oxygen and the maximum amount of water vapor at 
the given temperature. In such a mixture, each gas shares the total 
atmospheric pressure. Hence the actual pressure exerted by the 
oxygen is found by subtracting the pressure of the water vapor (found 
in the table) from the total pressure (indicated by the barometer). 
The corrected pressure is used in the formula for reducing the volume 
of a gas to its volume at 0° C. and 760 mm. (65). 



68 PRACTICAL CHEMISTRY 

75. Chemical conduct of water. — We have already seen 
that water at ordinary temperatures interacts with cer- 
tain metals, especially calcium, sodium, and potassium, 
and at higher temperatures with iron (49). Water is de- 
composed to some extent into its component elements (oxy- 
gen and hydrogen) by intense heat ; at about 2000° C. 
the. decomposition is less than 2 per cent. As the tem- 
perature falls, the elements recombine to form water. In 
other words, water is a stable substance towards heat. 

Water combines directly with many oxides. Thus^ 
lime, which is calcium oxide, combines directly with water 
and forms calcium hydroxide ; this chemical change is 
often attended by considerable heat, as may be seen when 
mortar is being prepared. Similarly, sulphur dioxide forms 
the compound sulphurous acid. These chemical changes 
may be represented thus : — 

Calcium Oxide -j- Water = Calcium Hydroxide 

(Calcium-Oxygen) (Calcium-Hydrogen-Oxygen) 

Sulphur Dioxide + Water = Sulphurous Acid 
(Sulphur-Oxygen) (Sulphur-Hydrogen-Oxygen) 

Such oxides are called anhydrides. 

Water combines with certain solids when they separate 
from a solution by crystallization. Thus, from a solu- 
tion of copper sulphate blue crystals are obtained, which 
when heated give off water and crumble to a gray white 
powder. (See Water of Crystallization, 83.) 

76. Solvent power of water. — Water dissolves a great 
many substances, i.e. they disappear when put into w^ater. 
The liquid which results from this process of dissolving is 
called a solution. The dissolved substance is distributed 
uniformly throughout the whole liquid and will not settle 
out. The liquid in which the substance dissolves is called 



WATER 69 

the solvent. The dissolved substance is called the solute. 
A water solution of a substance is sometimes called an aque- 
ous solution — the kind we are considering in this chapter. 
Substances differ widely in their solubility. A solution 
which contains a small proportion of solute is called a dilute 
solution ; one containing a large proportion of solute is 
called a concentrated solution. 

77. Solution of gases. — Water dissolves many gases. 
Some like ammonia, are very soluble, while others, such as 
oxygen and nitrogen, are only shghtly soluble. Air dis- 
solves sHghtly in water. Thus, if faucet water, or water 
that has been shaken in a bottle, is heated, bubbles gather 
and escape as the heat is increased. As a rule, the solu- 
bility of a gas decreases with rise of temperature. Pres- 
sure, too, influences the solubility of gases. Thus, as we 
have already seen (36), carbon dioxide is forced into 
cyHnders of water in preparing soda water. W^hen the pres- 
sure is decreased by opening the valve, the gas escapes 
rapidly and causes the soda water to froth or foam. 
Bubbles caused by escaping carbon dioxide may also be 
seen when the stopper is removed from a bottle containing 
a charged beverage (Figs. 14, 15). 

This rapid escape of a gas is called effervescence. 
Underground waters often contain considerable carbon 
dioxide, owing to the great pressure to which subterra- 
nean gases are subjected. Hence, many natural mineral 
waters effervesce when they come to the surface. 

78. Solutions of liquids. — Some liquids, such as alcohol 
and glycerin, dissolve in water in all proportions ; others, 
e.g. gasolene and kerosene, are very slightly soluble, as is 
shown by the fact that after agitation with water they sep- 
arate almost entirely as distinct layers of oil and water. 

Some Uquids dissolve to a limited extent in water. Ether 



yo PRACTICAL CHEMISTRY 

is an example. If ether is shaken with water and the liquid 
is allowed to stand a short time, two layers form. The 
upper layer consists of ether and a httle water ; the lower 
layer is the opposite. 

On the other hand alcohol and water form no such 
layers, not simply because each is soluble in the other, but 
because each is soluble without limit in the other ; that is, 
alcohol- water is a case of perfect mutual solubility, whereas 
ether-water is a case of limited solubility. 

79. Solutions of solids. — Water dissolves many sohds, 
and such solutions are very useful. The solubility of solids 
in water is a matter of the utmost practical im.portance, not 
only in its far-reaching effect in nature but also in its 
indispensable use to man. 

The solubihty of sohds in water depends on the substance. 
Some, like sand, dissolve scarcely at all and are often 
described as insoluble. Others, like salt, are moderately 
soluble, while still others, like magnesium chloride or sodium 
hydroxide, are highly soluble. 

The degree of solubility depends on temperature. In 
most cases solubihty increases with rise of temperature ; 
hence the common practice of heating to hasten solution. 
A few sohds (e.g. calcium hydroxide) are less soluble in 
hot water than in cold, and a few others (e.g. sodium chlo- 
ride) dissolve to about the same degree in hot and cold 
water. 

There is a limit to the solubility of most substances. As 
a general rule, a given weight of water at a fixed tempera- 
ture will dissolve only a definite weight of solid ; and this 
is the case, even though more undissolved sohd is available 
for solution. A solution conforming to the conditions 
just stated is said to be saturated. For general purposes, 
solubility may be expressed by such terms as insoluble, 



WATER 



71 



Table of the Solubility of Solids ix Water 



Solids 


Number of Gr.\ms in Solution in 100 Grams of Water 


20° C. 


100° C. 


Calcium chloride 
Calcium hydroxide 
Magnesium sulphate 
Potassium dichromate 
Potassium, nitrate 
Sodium chloride 


74-5 
0.165 
36.2 
13.0 
31.6 
36.0 


159.0 
0.077 

73.8 
102.0 
246.0 

39.8 



slightly soluble, or very soluble. It is more accurate to 
represent the amount of solvent by loo gm. ; on this basis 
the solubihty of a sohd is the number of grams of soHd dis- 
solved by 100 gm. of water. 

80. Solubility tables and curves. — The accompanying 
table of solubihty shows the solubihty of some solids. But 
this table is hmited, only two temperatures being given. 

A better way of representing the solubihty of a sub- 
stance is by a solubihty curve. The curves of several 
substances are shown in Fig. 43. The temperature is read 
along the vertical lines and the number of grams of solute in 
100 gm. of water along the horizontal lines. Many facts can 
be read from solubihty curves. For example, if we wish to 
know the temperature at which 40 gm. of potassium chlorate 
are held in solution by 100 gm. of water, it is only necessary 
to find where the horizontal hne numbered 40 cuts the 
potassium chlorate curve, and then follow the vertical 
line down to the temperature number, where 80° C. is found. 

81. Solution and crystallization. — If hot solutions are 
cooled or if enough of the solvent is removed by evaporation^ 
the solute separates from the solvent in crystals. The 
process of separating a dissolved solid from its solution by 



72 



PRACTICAL CHEMISTRY 




40' 50^ 
Temperature 
Fig. 43. — Solubility curves 

either of these ways is called crystallization. The shape 
and color of the crystals are characteristic of the particular 
substance and serve to identify it. Thus, common salt 
crystallizes in white cubes. (See also 83.) 

82. Supersaturated solutions. — Crystals are not always 
deposited from a cooled or a concentrated solution, as just 
stated. Thus, a hot, very concentrated solution of some 
soHds, such as sodium sulphate or sodium thiosulphate, 
deposits no crystals when the clear solution cools, although 
the solution actually contains more solute than the solvent 



WATER 



73 



could ordinarily dissolve at the lower temperature ! Solu- 
tions which contain more solute than is needed for normal 
saturation are called supersaturated. Supersaturation oc- 
curs only under special conditions. For example, if a super- 
saturated solution is stirred or vio- 
lently shaken, crystals begin to 
form. Moreover, if a fragment of 
the solid is dropped into the super- 
saturated solution, crystals very 
quickly form upon the fragment 
and soon accumulate in a conspic- 
uously large quantity (Fig 44). 



m 



o 



^ 



H 



Fig. 44. — Experiment illus- 
trating supersaturation 



Supersaturation can be shown by a simple experiment. A test tube 
containing two or three cubic centimeters of water and considerable 
crystallized sodium thiosulphate is heated until a solution is produced. 
The clear solution is then poured into a warm test tube, a cork or wad 
of cotton is inserted, and the solution is allowed to cool. It remains 
clear. Now if a fragm.ent of a crystal of the solid is dropped in, the 
crystals soon form and may become a solid mass. In Fig. 44 the 
successive stages are shown. 



83. Solution and water of crystallization. — Crystals of 
some solids contain water, which is an essential part of the 
compound. The combined water must not be confused 
with water which adheres to a crystal or is inclosed in it. 
Crystals containing combined water are dry even after 
the crystals are powdered. The combined water can be 
removed by heat or sometimes merely by exposure to air. 
Loss of water is usually attended by loss of color and always 
by loss of crystalHne appearance. Thus, crystallized cop- 
per sulphate loses its blue color slowly at ordinary tempera- 
tures and very rapidly when heated, finally becoming a 
gray powder. 



74 PRACTICAL CHEMISTRY 

The proportion of combined water in crystals is constant 
in the same compound, but in different substances the 
proportion varies between wide hmits. Water chemi- 
cally combined in a crystal and readily removed in a 
definite proportion by heating is called water of crystal- 
lization. 

Compounds containing water of crystallization are some- 
times called hydrates or hydrated compounds. Conversely, 
compounds which have been deprived of water of crystalli- 
zation are said to be anhydrous or dehydrated. For ex- 
ample, blue crystallized copper sulphate is a hydrate of the 
compound copper sulphate ; but after the blue compound 
has been heated, it is anhydrous or dehydrated copper 
sulphate, which is a gray powder. Anhydrous compounds 
often readily become hydrated again. Thus, when the 
gray anhydrous copper sulphate is added to water, a blue 
solution is produced from which blue crystals of hydrated 
copper sulphate are readily obtained. 

84. Efflorescence. — Some crystallized substances lose 
water of crystallization merely by exposure to air and be- 
come powders. This property is called efflorescence, 
and such substances are said to be efflorescent or to 
effloresce. Crystals of washing soda, alum, and borax 
effloresce readily. 

An explanation of efflorescence is found in the principle of vapor 
pressure. Solids containing water of crystallization exert a slight 
vapor pressure. If this vapor pressure is greater than the pressure of 
the water vapor in the atmosphere, the substance loses water until 
the vapor pressures are equal or until all the water has escaped from 
the substance. On the other hand, some substances containing water 
of crystallization do not effloresce because their tendency to lose water 
is counteracted by the water vapor in the air. Crystallized barium 
chloride and gypsum belong to the latter class. 




WATER 75 

85. Deliquescence. — Many substances when exposed to 
air become moist, and sometimes even dissolve in the ab- 
sorbed water. Calcium chloride, potassium carbonate, 
zinc chloride, sodium hydroxide, and potassium hydroxide 
belong to this class. This property is called deliquescence 
and the substances are said to deli- 
quesce, or to be deliquescent. Deli- 
quescence is a property of very soluble 
substances. Common salt often deli- 
quesces, especially in damp weather, 
owing to small quantities of magnesium 
and calcium chlorides which are present 

as impurities. The property of deli- / ' 

quescence is utilized in the laboratory '^^-^:^^:^-^ 

to dry substances, calcium chloride Fig. 45- — A desiccator 

1 . r. 1 J r iU' containing calcium 

being often employed for this purpose. ^^,^^.j^ ^.^ ^^^ ^^^_ 
One form of apparatus used is called torn) 
a desiccator (Fig. 45) . 

Deliquescence is readily explained. Water vapor from the air 
condenses on the surface of the solid and produces a very concentrated 
solution, which has a vapor pressure much lower than the average 
pressure of the water vapor in the air ; the solution, therefore, con- 
tinues to take up water until its vapor pressure equals the pressure of 
the water vapor in the air. 

86. What is a solution ? — Let us try three experiments : 
(i) If we shake a httle salt with water, the salt dissolves. 
We have a solution, i.e. a mixture in which the salt is uni- 
formly distributed and from which the salt will not settle 
out. (2) If we shake a Httle powdered starch with cold 
water, the starch is distributed more or less uniformly 
throughout the liquid. But on standing, the starch begins 
to settle out, and finally the mixture separates into water 
and starch. The starch was not dissolved, but merely 



76 PRACTICAL CHEMISTRY 

suspended in the water. Such a mixture of a soHd and 
water is called a suspension. (3) If we shake kerosene 
oil vigorously with water, the oil breaks up into fine drops 
which are distributed throughout the liquid. After a time, 
however, the oil separates from the water. Such a mix- 
ture of a liquid and water is called an emulsion. 

Suspensions and emulsions have a common property, 
viz. sooner or later the substance separates from the w^ater. 
On the other hand, the substance does not separate from 
a solution. This distinctive property of a solution, viz. 
absence of settling, is doubtless due to the fact that in a 
solution the dissolved particles are exceedingly minute 
— too minute to be seen through a microscope or detected 
by a beam of hght. It w^as found many years ago that if 
a beam of Hght is passed into a dark room, the path is re- 
vealed by the dust particles that reflect the light; this 
effect may be seen when a sunbeam comes through an 
opening in a blind or a hole in a curtain. But when a strong 
beam of light is passed through a solution, no bright path 
is revealed, because the dissolved particles are much too 
small to reflect light. 

Certain substances, however, form clear mixtures with 
water from which the substance does not settle nor can it 
be removed by filtering. These liquids look homogeneous, 
i.e. all parts appear to be just alike. And yet, if we pass 
a beam of hght through them, the path is bright, thereby 
proving that these mixtures contain particles in suspension. 
Such mixtures are not true solutions, but colloidal solutions, 
i.e. mixtures in which the particles in suspension are very 
fine — only a little coarser, in fact, than the particles in 
a true solution. Colloidal solutions should really be called 
colloidal suspensions, but the term solution is often used. 
Many substances can be reduced to the colloidal state. 



WATER 77 

They are called colloids. Typical examples are starch 
(349), silicic acid (389 1, clay, and metals like gold. (See 
especially 101.) 

In true solutions, then, the particles of the solute are in an 
exceedingly fine state of division. Whereas in suspensions 
and emulsions the particles are much larger — large enough 
to be seen through a microscope and often with the eye. 
Between these two classes come colloidal solutions ; in 
them the particles are too fine to settle out, though large 
enough to reflect light, ranging in size from those in true 
solutions to those in typical suspensions (101). In passing 
from true solutions through colloidal solutions to sus- 
pensions (and emulsions), the change is gradual, not abrupt, 
since the distinction seems to be based fundamentally on 
the size of the particles. 

87. Composition of water. — Water is a compound of 
hydrogen and oxygen. That is, its constituents are the 
elements hydrogen and oxygen, and they are chemically 
combined in a constant ratio. 

We have already learned in several ways that hydrogen and oxygen 
are constituents of water, (i) Metals, such as calcium, sodium, and 
iron, liberate hydrogen from water and form simultaneously com- 
pounds containing oxygen (49). (2) If an electric current is passed 
through an acid (or alkaline) solution of water, hydrogen and oxygen 
are liberated (16). (3) When hydrogen is burned iA air or in oxygen, 
water is produced (53). 

We can show by a simple experiment that oxygen is a 
chemical constituent of water. A tube about a meter long 
and closed at one end is completely filled with chlorine 
water (prepared by saturating water with chlorine — an 
element to be studied in Chapter XI). The open end is 
immersed in a vessel containing some of the same solution, 
and the whole apparatus is placed in the direct sunlight. 



78 



PRACTICAL CHEMISTRY 



The chlorine and water interact, forming hydrochloric acid 
and oxygen. Bubbles of gas soon appear in the liquid, 
and after a few hours a small volume of gas 
collects at the top of the tube (Fig. 46). 
The gas can be shown to be oxygen by the 
usual test, viz. relighting a glowing joss stick 
or splint of wood. 

88. Electrolysis of water. — The decom- 
position of water by electricity, or, as it is 
called traditionally, the electrolysis of water, 
shows by a single experiment that water con- 
sists of the elements hydrogen and oxygen. 
It is done in the laboratory in a special 
form of apparatus (Fig. 47). 




not conduct electricity, so a 
vols.) and 



Fig. 46. — Pre- 
paring oxygen 
from water by 
chlorine 



Pure water does 
Y~^"A^ J~\ mixture of water ( 

concentrated sulphuric acid (i 
vol.) is poured into the apparatus 
until the reservoir is half fidl 
(after the stopcocks have been 
closed) . 
As soon as an electric battery of three or more 
cells (or a reduced street current) is connected with 
the piece of platinum near the bottom of each 
tube, bubbles of gas appear on the platinum, rise, 
collect in the upper part of the tubes, and slowly 
force liquid from each tube into the reservoir. 

The volume of gas is greater in one tube than 
in the other, when the electrolysis is stopped. As- 
suming that the tubes have the same diameter, the 
gas volumes are in the same ratio as their heights, 
which will be found by measurement to be ap- 
proximately two to one. Tests applied to each gas 
(by letting a little out through the stopcock) show 
that the gas having the larger volume is hydrogen pig. 47. 




and that the other gas is oxygen. 



Elec- 
trolysis of water 



WATER 



79 



89. How the exact composition of water is found. — 
The experiments just cited and described show the 
qualitative composition of water. That is, they show that 
water is a compound of the two elements hydrogen and 
oxygen. But they give us no information about the propor- 
tion of the elements in the compound. To find the quan- 
titative composition of 
water, we must study the 
results of experiments per- 
formed for the purpose of 
determining the exact pro- 
portions — " the quan- 
tity " — in which the two 
elements combine to form 
the compound. 

Since the constituents 
of water are gases, we can 
find the composition by 
volume, i.e. volume tri- 
cally, as well as by weight, 
i.e. gravimetrically. More- 
over, we can determine the 
quantitative composition 
by analysis, i.e. taking the compound apart chemically, or 
by synthesis, i.e. putting its parts together chemically. 

90. Morley's determination of the gravimetric compo- 
sition of water by synthesis. — The most accurate deter- 
mination of the gravimetric composition of water ever 
made was completed by the American chemist Morley 
in 1895 (Fig. 48). In his experiments he not only weighed 
the hydrogen and oxygen that combined but also the water 
formed by their synthesis. 

The apparatus (Fig. 49) was weighed vacuous {i.e. free 




Fig. 48. — Morley (1838 ) 



8o 



PRACTICAL CHEMISTRY 



5\ 



u& 



from air or other gases). The tubes aa were connected 
with the weighed reservoirs of pure oxygen and hydrogen, 
and the oxygen was introduced. Sparks were next passed 
between the platinum wires cc, and the heat 
ignited the hydrogen, which was slowly ad- 
mitted, the combination of gases taking place 
at bb. The water vapor condensed in the tube 
dd, the lower portion of which was immersed 
in cold water. The combustion of the hydro- 
gen was continued until a suitable weight of 
water was formed. The introduction of the 
gases was then stopped. The water and its 
vapor were then converted into ice by putting 
the apparatus into a freezing mixture. The 
gases left over when the combustion was stopped 
were drawn off, passing in their exit through 
tubes of phosphorus pentoxide in ee which re- 
tained all traces of water. This mixture was 
M or ley's analyzed and allowance made for the hydrogen 
apparatus ^^ oxyffcn in it. The whole apparatus, freed 

for deter- , , ^, , r n • -u j 

mining the ^ ^om hydrogen and oxygen, was finally weighed ; 
gravimet- the increase was the weight of water formed by 
ric com- ^Yie combination of known weights of hydrogen 
water^" ° and oxygen. As the result of exceptionally ac- 
curate experiments Morley found that i part 
by weight of hydrogen combines with 7.9395 parts by 
weight of oxygen. 

91. Dumas' determination. — Another method was used by the 
famous French chemist Dumas in 1843. It consisted in passing dry 
hydrogen over heated copper oxide. We have seen (55) that in this 
chemical change hydrogen reduces copper oxide and thereby forms 
copper and water. If the copper oxide and copper are weighed, the 
loss is the weight of the oxygen used. If the water is collected and 
weighed, the difference between the weights of the water formed and 



Fig. 49. 



WATER 



8i 



the oxygen used is the weight of the hydrogen. The result obtained 
by Dumas has long ceased to be regarded as accurate, but the de- 
termination has historical interest. 

92. The volumetric composition of water. — The electrol- 
ysis of water is good evidence that the volumetric compo- 
sition of water is 2 of hydrogen to i of oxy- 
gen. An accurate determination is made by 
synthesis, i.e. by measuring accurately the 
volumes of hydrogen and oxygen that com- 
bine to form water. A sketch of one form of 
apparatus is shown in Fig. 50. The essential 
part is the eudiometer A. It is a graduated 
glass tube closed at the upper end. Near this 
end two platinum wires are fused into the 
glass ; the outer ends are looped and the inner 
ends are near together so that an electric 
spark will leap across the gap and produce 
enough heat to cause the two gases to unite. 




Fig. 50. — Ap- 
paratus for 
determining 
the volumet- 
ric compo- 
sition of 
water 



The experiment is readily performed. The eudiom- 
eter is filled with mercury and inverted in the jar 
of the same liquid. Hydrogen is introduced until 
the eudiometer is about one fourth full. The mer- 
cury levels inside and outside are made the same, and 
the volume of hydrogen is read accurately. The temperature and 
pressure are also read. Approximately an equal volume of oxygen is 
introduced, the levels are adjusted, and the total volume read accu- 
rately. Each volume is corrected for temperature and pressure. 
The difference between the two corrected volumes is the volume of 
oxygen. An excess of oxygen is needed to lessen the violence of the 
explosion ; this excess takes no part in the chemical change. 

The combination of the two gases is caused by connecting the 
looped ends of the platinum wires with an induction coil and battery, 
and .passing a spark across the gap. A slight explosion indicates 
combination. The mercury, after the shock from the explosion, 
rises and nearly fills the eudiometer. The volume of water is too 



82 



PRACTICAL CHEMISTRY 






(>=c^ 



minute to measure in this apparatus. After the mercury and re- 
sidual gas (oxygen) are cool, the levels are adjusted, and the volume 
of gas is read (as well as the temperature 
and pressure). The corrected volume of 
this gas is subtracted from the volume of 
oxygen originally introduced, thus giving 
the actual volume of oxygen that combined 
with all the hydrogen to form water. 

An example will make this experi- 
ment clear. Suppose the corrected 
volumes were : — 

Volume of hydrogen added . . 22.3 cc. 

Volume of hydrogen and oxygen 

added 41.5 cc. 

Volume of oxygen added . , 19.2 cc. 

Volume of oxygen left ... 8.0 cc. 

This means that 19.2 — 8, i.e. 11. 2 
cc. of oxygen were actually used. 
In other words the two gases com- 
bined in the ratio of 22.3 to 11. 2, or 
very nearly 2 volumes of hydrogen 
to I volume of oxygen. 

Very exact experiments show that 
the volumetric ratio of hydrogen to 
oxygen in water is 2.00268 to i. 

93. Gay-Lussac's law of gas vol- 
umes. — A modification of the ex- 
periment described in 92 shows that 
2 volumes of water vapor are formed 
when 2 volumes of hydrogen and 
I volume of ox}^gen unite. In the 
apparatus (Fig. 51) the eudiometer is surrounded by a large 
tube through which steam is passed, thereby preventing 
the condensation of the water vapor. If 2 volumes of hy- 




Fig. 51. — Apparatus for 
showing that 2 vol- 
umes of water vapor 
are formed by explod- 
ing 2 volumes of hy- 
drogen and I volume 
of oxygen 



WATER 



83 



drogen and i volume of oxygen are exploded, 2 volumes of 
water vapor are formed — provided all the gases are meas- 
ured at the same pressure and the same temperature (about 
100° C). This result means that the volumes of hydrogen, 
oxygen, and steam are expressed by 2, i, and 2, i.e. by small 
whole numbers. 

When other chemical changes involving gases are studied, 
similar simple relations are found. This general fact, which 
was discovered by the 
French chemist Gay- 
Lussac (Fig. 52), in 1808, 
may be stated as a law, 
thus : — 

In a chemical change 
the volumes of the gases 
can he expressed by s?nall 
whole numbers. 

This law will be used 
in a later chapter (XV ; 
see also 157, 176). 

94. Summary of the 
composition of water. — 
Experiments show that 
water consists of the two 
elements hydrogen and 
oxygen combined in a fixed ratio by weight, viz. i to 7.9395 ; 
they are also combined in the ratio of 2.00268 to i by 
volume. Usually these ratios are stated approximately as 
2 to 16 by weight and 2 to i by volume. Often the gravi- 
metric composition of water is stated inper^cent, viz. 11. 18 
per cent of hydrogen and 88.82 per cent of oxygen. Some- 
times, we say, briefly, water is ^ hydrogen and f oxygen. 

95. Hydrogen peroxide. — Hydrogen peroxide is a com- 




Gay-Lussac (i 778-1850) 



84 PRACTICAL CHEMISTRY 

pound of hydrogen and oxygen. But the proportion of the 
constituents is not the same as in water. Water consists 
of 1 1. 1 8 per cent of hydrogen and 88.82 per cent of oxygen, 
whereas hydrogen peroxide consists of 5.88 per cent of 
hydrogen and 94.11 per cent of oxygen. Stated diflerentiy, 
water consists of 2 parts of hydrogen and 16 parts of oxygen, 
and hydrogen peroxide of 2 parts of hydrogen and 32 parts 
of oxygen — all parts by weight. If we compare the comx- 
position of water and hydrogen peroxide, we see that in 
hydrogen peroxide there is twice as much oxygen as in water. 
This fact is brought out in the old name hydrogen dioxide, 
which is sometimes used now. 

The two compounds, water and hydrogen peroxide, are a good 
example of the law of multiple proportions (47). 

Hydrogen peroxide is a colorless Hquid which dissolves 
readily in water. It is sold usually as a 3 per cent solution, 
which has a rather sharp odor and a metallic taste. The 
hydrogen peroxide decomposes slowly into oxygen and 
water. Hence it is an oxidizing agent. It is used to bleach 
{i.e. whiten) hair, feathers, fur, silk, ivory, and bone. It 
destroys bacteria and is used as an antiseptic, e.g. in cleans- 
ing wounds, though its effectiveness is often overestimated. 

EXERCISES 

1. Prepare a summary of (a) the properties of water and (b) the 
composition of water. 

2. Topics for home study, (a) Purification of drinking water. 
(b) Distillation, (c) Water as an erosive agent, (d) Crystals, 
(e) Vapor pressure. (/) Chemical conduct of water. 

3. Define and illustrate (a) water of crystallization, (b) efflores- 
cence, (c) deliquescence, (d) anhydrous, (e) dehydrated. 

4. Define and illustrate (a) solution, (b) solvent, (c) solute, (d) di- 
lute, (e) concentrated, (/) unsaturated solution, (g) saturated solution, 
(h) supersaturated solution, (i) solubility, (j) solubility curve. 



WATER 85 

6. Practical topics, (i) How would you prove that a given liquid 
is pure water? (2) What conditions are favorable for (a) evaporation, 
(b) efflorescence, (c) deliquescence? (3) Suggest experiments (a) to 
find the solubility of a solid in water at 40° C, {b) to show that water 
from a crystal is not water of crystallization, (c) to find the per cent of 
water in a potato. (4) Why is sea water salt? How might sea water 
be rendered suitable for drinking? 

6. State {a) the volumetric and (b) the gravimetric composition 
of water. How is each found? 

7. What do these show about the composition of water: (a) La- 
voisier's experiment (49)? (b) Burning of hydrogen? (c) Elec- 
trolysis of water? 

8. Describe ]\Iorley's experiment on the composition of water, 

9. State and illustrate Gay-Lussac's law. 



PROBLEMS 

1. Find the volume of the dry gas at 0° C. and 760 mm. in : 
(a) 80 cc. at 760 mm. and 17° C. ; (b) 80 cc. at 745 mm. and 19° C. ; 
(c) 100 cc. at 765 mm. and 17.5° C. ; (d) 97 cc. at 757 mm. and 20.5° C. 

2. Plot the following data on cross section paper and draw the solu- 
bility curve of the substance : Temperature — o, 10, 20, 30, 40, 50, 55 ; 
corresponding solubility (i.e. number of gm. soluble in 100 gm. of water) 
— 13, 21, 31, 45, 64, 86, 100. 

3. If the density of ice is 0.92, what volume will a liter of water 
at 4° C. occupy w^hen frozen? Ans. 1.087 1- 

4. By the use of the solubility curves in Fig. 43 answer the follow- 
ing : (a) How many gm. of sodium chloride are in solution at 20°, 
30°, 55°, 65°, 0°, 100° ? {b) At what temperatures are 60 gm. and 
95 gm. of potassium bromide in solution? (r) Compare the solu- 
bility of sodium nitrate and sodium chloride. How much of each is 
in solution at 20'', 25°, 30°? 

5. Calculate the per cent of water of crystallization in each crystal- 
lized substance from the following : (a) 5 gm. of aluminium sulphate 
lose 2.43 gm. on heating ; (b) 7 gm. of calcium sulphate lose 1.464 gm. ; 
(c) 3 gm. of cadmium nitrate lose 0.7 gm. ; (d) 3 gm. of cobalt nitrate 
lose 1. 113 gm. 

6. Suppose 15 gm. of water are decomposed. What weight of 
(a) oxygen and (b) hydrogen is produced? What volume (at 0° C. and 
760 mm.) of (c) oxygen and (d) hydrogen? 

7. What volume of oxygen (at 0° C. and 760 mm.) must be used 
to unite with 175 gm. of hydrogen to form water? 



86 PRACTICAL CHEMISTRY 

8. What volume of hydrogen (at o° C. and 760 mm.) must be used 
to convert 175 gm, of oxygen into water? 

9. A mixture of 500 cc. of oxygen and 1250 cc. of hydrogen (both 
at 0° C. and 760 mm.) is exploded. What weight of water is formed? 
Ans. 0.805 S'^- 

10. 50 cc. of oxygen are mixed with 500 cc. of hydrogen, both 
measured at the normal temperature and pressure. x\n electric spark 
is passed through the mixture. What volume, if any, of gas will re- 
main, and how would you ascertain whether it is hydrogen or oxygen? 



CHAPTER VII 

LAW AND THEORY — LAWS OF DEFINITE AND MULTIPLE 
PROPORTIONS — ATOMIC THEORY — ATOMS AND MOLE- 
CULES-ATOMIC WEIGHTS 

96. Facts, laws, and theories. — The facts we study in 
chemistry were discovered by observation and experiment. 
Facts which always occur under the same conditions soon 
become well estabhshed. Many related facts are often 
summarized in a brief general statement called a law. The 
explanation we give of facts, especially groups of related 
facts, is called a theory. 

Laws and theories are of great service in chemistry, since 
they help us gather into inteUigible statements our knowl- 
edge of a vast number of related facts. They also help 
us discover new facts and interpret phenomena. 

In this chapter wq shall review^ three laws already studied, 
and interpret them by a theory called the atomic theory. 

97. Law of the conservation of matter. — We have seen 
(5) that in a chemical change the total weight of the mat- 
ter involved is not altered. That is, the sum of the weights 
of the substances entering into a chemical change always 
equals the sum of the weights of the substances resulting 
from the chemical change. This general fact about chemi- 
cal change is summed up by the law of the conservation 
of matter, thus : — 

No iveight is lost or gained in a chemical change. 
Sometimes this law is stated in another form, viz. mat- 
ter is indestructible. 

87 



88 PRACTICAL CHEMISTRY 

98. Law of constant composition. — We learned in 9 
that constant composition is an essential characteristic 
of a compound, e.g. water contains 88.82 per cent oxygen 
and 1 1. 18 per cent hydrogen. Experiments show that in all 
chemical compounds the different constituents are present 
in a definite and constant proportion by weight. This 
general fact, stated in the form of a law, becomes the law 
of constant composition or the law of definite proportions, 
thus : — 

A given chemical compound always contains the same ele- 
ments in the same proportion by weight. 

99. Law of multiple proportions. — We saw in 47 that 
if the composition of different compounds of the same ele- 
ments is expressed in a special way, multiple relations exist 
between the weights of one constituent. Composition 
is usually expressed in per cent. But if a fixed weight of 
one constituent is adopted as a basis, and the composition 
of the compounds is expressed in terms of this weight, then 
the simple multiple relation which exists between the 
weights of the other constituent (or constituents) may be 
clearly seen. 

Consider this case. No multiple relation appears in the 
statement that the two compounds of carbon and oxygen 
consist respectively of 27.27 and 42.85 per cent of carbon 
and 72.72 and 57.14 per cent of oxygen. However, if we 
state these proportions in a different way, multiple re- 
lations will be clearly seen. We first reduce each propor- 
tion of carbon to i thus: 27.27 -^ 27.27 = i, and 42.85 
-^42.85 = I. But in order to maintain the correct relation 
of carbon to oxygen (found by analysis and expressed above 
as per cent) we must divide each proportion of oxygen by 
the corresponding number, i.e. 72.72 -^ 27.27 = 2.6, and 
57.14 -r- 42.85 = 1.3. These two operations give us: — 



LAW AND THEORY 



89 



Ratio of carbon i to i 
Ratio of oxygen 2.6 to 1.3 

Now 2.6 and 1.3 are in the ratio of 2 to i. Obviously 
the weights of oxygen in the carbon oxides are in a 
simple multiple relation. 

The general fact of multiple proportions is expressed as 
the law of multiple proportions, thus : — 

When elements unite to form a series of compounds, a fixed 
weight of one element always combines with such weights of the 
other element {or elements) 
that the ratio between these 
diferent weights can be 
expressed by sm.all whole 
numbers. 

100. The atomic the- 
ory. — The theory that 
explains the facts sum- 
marized in the three fun- 
damental laws just re- 
viewed is called the 
atomic theory. It was 
proposed about 1805 by 
the English chemist Dal- 
ton (Fig. 53). According 
to this theory: (i) an 
element is made up of a vast number of very small particles 
called atoms; (2) atoms of the same element have the 
same weight ; (3) atoms of different elements dij6fer from 
one another in weight; (4) chemical change is the union, 
separation, or exchange of whole atoms. The atomic the- 
ory means in a few words that matter is composed of 
atoms, which remain undivided in chemical changes. 




Fig. 53. — Dalton (i 766-1844) 



90 PRACTICAL CHEMISTRY 

With the help of the atomic theory, many facts about 
elements, compounds, and chemical change can be made 
very much clearer. 

101. Atoms and molecules. — An atom is the smallest, 
indivisible particle of an element. In a chemical change 
the atom is the vehicle. It is the smallest part of an ele- 
ment which participates in a chemical change. If two 
or more atoms are held together by chemical attraction, 
the product of this combination of atoms is called a mole- 
cule. If the atoms are alike, the molecule is a molecule of 
an element, e.g. a molecule of oxygen consists of two atoms 
of the element oxygen (O2). If the atoms are not alike, 
the molecule is a molecule of a compound, e.g. a molecule 
of water consists of two atoms of hydrogen and one of oxy- 
gen (H2O). A molecule of a compound always contains 
one or more atoms of different elements ; hence, we may 
think of such molecules as the smallest particles of the 
compound. Thus, a molecule of water is the smallest 
particle of the compound water because if we try to pro- 
duce a smaller particle, we obtain atoms of the elements 
hydrogen and oxygen. 

Although atoms and molecules are exceedingly small, 
too small to be seen by direct observation, nevertheless 
certain experiments give conclusive evidence of their exist- 
ence. Atoms will be considered later ; we can consider 
molecules now. 

We found in 66 that certain properties of gases can be 
readily and adequately explained by the kinetic-molecular 
theory, i.e. the supposition that gases consist of exceedingly 
minute, rapidly moving particles called molecules. 

Are there molecules in a liquid? When a colloidal solu- 
tion (86) is examined with an ordinary microscope under 
favorable conditions, tiny moving points of light are seen. 



LAW AND THEORY 



91 




If an ultra-microscope is used, the result is startling. The 
tiny points of light seen in the liquid dart about with a zig- 
zag motion. An ultra-microscope is one arranged so we 
can look down against a dark background into the liquid 
through which a beam of strong light is 
sent horizontally. These moving points 
are colloidal particles, which, although 
invisible, reveal their presence by re- 
flected light. 

The path traversed by one of these 
points seen in a colloidal solution is com- 
pHcated (Fig. 54). This motion, which 
is called the Brownian movement, is 
seen in all colloidal solutions regardless 
of the nature of the particles (though 
seen best with finest particles) or the age 
of the solution. The erratic movement 
of the colloidal particles is due to the 
ceaseless, irregular bombardment of the 
particles by the molecules of water. The movements and 
the size of the colloidal particles have been carefully investi- 
gated, and the results furnish conclusive evidence of the 
existence of molecules in solutions. 

102. Interpretation of chemical change by the atomic 
theory. — Let us picture a chemical change in terms of the 
atomic theory, e.g. the combination of copper and oxygen. 
A piece of the element copper consists of many miUions of 
atoms of copper ; a mass of oxygen likewise consists of a 
very large number of atoms of oxygen. When the chem- 
ical change occurs between copper and oxygen, atoms of 
copper combine with atoms of oxygen and form molecules 
of the compound copper oxide. And this combining of 
atoms into molecules continues until all the atoms of cop- 



Fig. 54. — Path of a 
colloidal particle 



92 PRACTICAL CHEMISTRY 

per or all the atoms of oxygen (or under certain conditions 
all the atoms of both substances) have been used up. Sim- 
ilarly, the decomposition of mercury oxide is the sepa- 
ration of numberless molecules of the compound mercury 
oxide into atoms of the elements mercury and oxygen. So 
also, the liberation of hydrogen from sulphuric acid is 
the exchange of atoms of zinc for the atom.s of hydrogen in 
the compound sulphuric acid. 

103. How the atomic theory assists us in explaining 
the three fundamental laws of chemical change. — These 
laws, we have already found, are the law of the conser- 
vation of matter, the law of constant composition, and the 
law of multiple proportions. 

Let us take first the law of the conservation of matter, 
viz. unvarying weight in a chemical change. According 
to the atomic theory the weight of an atom is never changed. 
In the case of copper and oxygen and all other chemical 
changes, no atoms are created or destroyed ; they are merely 
redistributed on another plan. Nor are atoms changed 
in weight; the weight of the copper oxide formed equals 
the sum of the weights of the copper and oxygen used up. 
Inasmuch as all chemical changes have this character- 
istic, viz. unvarying total weight, it is obvious that the 
atomic theory, which assumes unchanging weights of atoms, 
is in accord with the law of the conservation of matter. 

Second, we consider the law of constant composition, 
viz. a given compound always consists of the same elements 
in a fixed proportion. According to the atomic theory, 
molecules are formed by the union of some whole number 
of atoms of an element with some whole number of atoms of 
another element or elements. Each molecule of the com- 
pound copper oxide, for example, would therefore consist 
of one or more atoms of copper united with one or more 



LAW AND THEORY 93 

atoms of ox>^gen, and the composition of each molecule 
of copper oxide would be constant, i.e. each molecule would 
consist of the same elements united in a constant ratio by 
weight. This means that the composition of copper oxide 
would always be a certain per cent of copper and a certain 
per cent of oxygen. Since all other chemical compounds 
have been found to have a constant composition, the atomic 
theory is in harmony with the law of constant composition. 

Finally, we interpret the law of multiple proportions, 
viz. simple multiple relations exist between the weights 
of one of the constituents of a series of compounds. Ac- 
cording to the atomic theory atoms are transferred as 
wholes ; this means there are no fractions of atoms. Con- 
sider the two oxides of carbon. Each contains carbon 
and oxygen in a definite ratio, but the ratios are different. 
In one the ratio of carbon to oxygen is i to 1.33, and in the 
other I to 2.66 (99). That is, there is twice as much oxy- 
gen combined with carbon in one case as in the other. In 
other words, if a molecule of one compound consists of 
one atom of carbon and one of ox}^gen, a molecule of the 
other consists of one of carbon and two of oxygen. Since 
other series of compounds exhibit a simple multiple rela- 
tion, the atomic theory agrees with the law of multiple 
proportions. 

104. Atomic v/eights. — According to the atomic theory 
atoms of the same element always have the same weight 
but atoms of different elements have different weights. 
This means (i) that an atom of oxygen, for example, 
throughout all its varied changes retains its weight, and 
(2) that this weight differs from the weight of other kinds 
of atoms. The weights of different kinds of atoms are called 
the atomic weights of the elements or briefly atomic weights. 
These weights have been determined by very accurate 



94 PRACTICAL CHEMISTRY 

experiment. A table giving the exact, as well as the ap- 
proximate, values can be found on the inside of the back 
cover of this book. 

Atoms are exceedingly small, so small, in fact, that no 
attempt is made to weigh a single atom. If, however, 
the proportions in which elements combine are reduced 
to a special standard, we obtain the relative weights 
of atoms. The standard atomic weight is oxygen = i6. 
The atomic weight of carbon is 12, of hydrogen i, of copper 
63.57. Other weights can be found in the table. 

The approximate atomic weights are accurate enough 
for general use, and the common ones should be learned. 

It must be remembered that the atomic weights are rela- 
tive weights. That is, the atomic weight of copper is 63.57, 
not 63.57 gm. or any other actual weight, but 63.57 ^s long 
as 16 is accepted as the standard atomic weight of oxygen. 

The exact determination of atomic weights is a difficult task. 
Several principles must be considered in making the final selection. 
Until this subject is discussed (see Chapter XVI), it will be well 
enough to regard atomic weights as the numerical values of the ele- 
ments in chemical changes and to select the approximate weights 
from the table as needed. 

EXERCISES 

1. Define law and theory as used in science. 

2. State the law of conservation of matter. Illustrate it by the de- 
composition of mercury oxide. 

3. State the law of constant composition. Illustrate it by the 
gravimetric composition of water. 

4. State the law of multiple proportions. Illustrate it by the 
two carbon oxides. 

5. State the four points in the atomic theory. 

6. (a) What is an atom? A molecule? (b) Discuss the relation 
of atoms to molecules. 

7. Describe a chemical change in terms of the atomic theory. 



LAW AND THEORY 95 

8. Interpret by the atomic theory the three laws: (a) conserva- 
tion of matter, (b) constant composition, (c) multiple proportions. 

9. What are atomic weights? 

10. Learn the approximate atomic weight of these elements : Hydro- 
gen, oxygen, nitrogen, carbon, copper, iron, sulphur, chlorine. 

11. As in E.xercise 10: Potassium, sodium, calcium, lead, mag- 
nesium, mercury, silver, zinc. 



CHAPTER VIII 



SYMBOLS AND FORMULAS 

105. What do symbols mean? — We learned in 12 that 
each element is designated by a symbol. Thus, O is the 
symbol of oxygen, C of carbon, H of hydrogen, Cu of copper. 

The symbols of the ele- 
ments are given in the 
table on the back inside 
cover. These symbols 
were introduced and first 
used extensively by the 
Swedish chemist 
Berzelius (Fig. 55). He 
analyzed many sub- 
stances and used the 
symbols to express the 
explicit relations of ele- 
ments and compounds 
in chemical changes. 

Symbols are not 
merely abbreviations of 
the names of the ele- 
ments. Each symbol stands for one atom of an ele- 
ment. Thus, H represents one atom of hydrogen. If 
more than one free atom is to be designated, the proper 
numeral is placed before the symbol. Thus, 2H means 
2 free atoms of hydrogen. If we wish to represent atoms 
in chemical combination, either with themselves or with 

96 




Fig. 5 



lius (i 779-1848) 



SYMBOLS AND FORMULAS 97 

other atoms, a subscript is used instead of a coefficient. 
Thus, H2 means 2 combined atoms of hydrogen, as in H2 

or H2O. 

Symbols not only represent atoms, but they also express 
atomic weights. Thus O represents an atom of oxygen 
which has the atomic weight 16. 

To sum up, a symbol has these meanings: (i) an ele- 
ment, (2) one atom of the element, (3) the atomic weight 
of the element. 

106. What are chemical formulas? We learned in 13 
that a formula is a group of symbols which expresses the 
composition of a compound. In writing a formula, the 
symbols of the atoms making up a molecule of the com- 
pound are placed side by side. Thus, CO is the formula 
of carbon monoxide, because one molecule of this compound 
consists of one atom each of carbon and oxygen. Whereas 
CO2 is the formula of carbon dioxide, because one mole- 
cule is composed of i atom of carbon and 2 atoms of 
oxygen. The symbols making up a formula might be 
written in different orders, but usage has determined the 
order in most cases. 

A formula represents one molecule. If we wish to des- 
ignate several molecules, we place the proper numeral 
before the formula. Thus, KCIO3 means i molecule and 
2KCIO3 means 2 molecules of potassium chlorate. Sim- 
ilarly, 2O2 means 2 molecules of oxygen each contain- 
ing 2 atoms. 

In certain compounds some of the atoms in a molecule 
act chemically like a single atom. This fact is ex-pressed 
by inclosing the group in a parenthesis, e.g. calcium hy- 
droxide has the formula Ca(0H)2 because the group OH 
often acts like an atom. Sometimes the parenthesis is 
replaced by a period, e.g. C2H5.OH (ethyl hydroxide) and 



98 PRACTICAL CHEMISTRY 

CUSO4.5H2O (copper sulphate pentahydrate (83)). The 
period and parenthesis are omitted if the composition of 
the compound is well understood, e.g. ammonium hy- 
droxide, NH4OH. 

If a group of atoms is to be multiplied, it is placed 
within a parenthesis. Thus, the formula of lead nitrate 
is Pb(N03)2. This means that the group NO3 is to be multi- 
plied by 2. The expression 2Pb(N03)2 means that the 
whole formula must be multiplied by 2. That is, in two 
molecules of lead nitrate there are 2 atoms of lead, 4 of 
nitrogen, and 12 of oxygen. 

Formulas are the outcome of experiments. We shall 
learn more about formulas. 

107. What do we mean by molecular weights? — Since 
a symbol stands for the atomic weight of an element, a 
formula stands for the sum of the atomic weights repre- 
sented by the group of symbols. This sum is called a molec- 
ular weight. In a few words, a symbol stands for an 
atomic weight and a formula stands for a molecular weight. 
Thus, the symbols H and CI stand for the atomic weights 

1 and 35.5 respectively, and the formula HCl stands for 
their sum i -f 35.5, or 36.5. If we know the formula of 
a compound, a simple way of finding the molecular weights 
is to add the atomic weights corresponding to the atoms 
in the formula. Using approximate values, the molecular 
weight of water (HoO) is 2 + 16 = 18. Similarly, the 
molecular weight of lead nitrate (Pb(N03)2) is 207 + 

2 (14 + 48) = 33^' 

108. How a formula expresses composition. — We have 
seen by several examples that the composition of a com- 
pound can be expressed in per cent and also by a formula. 
Thus, we can express the composition of w^ater by the 
formula H2O, and also by hydrogen = 11. 18 per cent and 



SYMBOLS AND FORMULAS 99 

oxygen = 88.82 per cent. How are these chemical and 
mathematical expressions related? The answer is simple. 
The symbols stand for numbers, and the mathematical ex- 
pression is the equivalent of the chemical formula. 

Suppose we have the formula of potassium chlorate, 
KCIO3, and we wish to express the composition in per cent. 
The process consists in transposing the chemical formula 
KCIO3 into the equivalent mathematical expression. This 
is done by : (i) dividing the weight of each element by the 
molecular weight and (2) multiplying the quotient by 100. 
Let us take an example. The formula KCIO3 stands for 
K = 39, CI = 35.5, and 3O = 48 {i.e. 3 X 16), or the 
molecular weight is 122.5. Then: — 



0.3184, or 31.84 per cent of potassium 



39 
122.5 

'^^'^ = 0.2898, or 28.98 per cent of chlorine 
122.5 

48 



122.5 



= 0.3918, or 39.18 per cent of oxygen 



Total 100.00 

The process of finding the composition in per cent from 
the formula is often called calculating the percentage com- 
position of a compound. 

109. The simplest formula of a compound can be calcu- 
lated from its percentage composition. — The calculation 
of a formula from the percentage composition is simply the 
process of finding the small whole numbers by which each 
atomic weight, as represented by its symbol, must be multi- 
plied in order to express the composition. The process is as 
follows: (i) divide each per cent by the corresponding 
atomic weight ; (2) reduce the quotients to whole numbers ; 
(3) write the formula. Let us take an example. The com- 
position of sulphuric acid is hydrogen = 2.04 per cent, 



lOO PRACTICAL CHEMISTRY 

sulphur = 32.65 per cent, oxygen = 65.31 per cent. If 
the percentage of each element is divided by the corre- 
sponding atomic weight, the quotients are 2.04, 1.02, and 
4.08. Reducing these quotients to whole numbers (by 
dividing by 1.02 in this case), the final quotients are 2, i, 4. 
These quotients represent the ratio of the atomic weights 
in a molecule of this compound. And since atoms are rep- 
resented by symbols, a molecule of sulphuric acid contains 
2 atoms of hydrogen, i of sulphur, and 4 of oxygen. This 
means that the formula of sulphuric acid must be H2SO4. 
Formulas calculated by this method are called simplest 
formulas. (See Determination of Molecular Formulas 
of Compounds, Chapter XV.) 



EXERCISES 

1. Prepare a summary of this chapter (a) in the form of short 
topics and (b) as a connected narrative. 

2. What three meanings do symbols have? 

3. Learn the symbols of these elements: (a) Aluminium, argon, 
barium, bromine, calcium, carbon, chlorine, copper, fluorine, gold. 
(b) Helium, hydrogen, iodine, iron, lead, magnesium, manganese, 
mercury, nitrogen, oxygen, (c) Phosphorus, potassium, silicon, silver, 
sodium, sulphur, tin, zinc. 

4. What elements correspond to C, CI, Ca, Cu, S, Si, Sn, ]SIg, Mn, 
Hg, H, He, A, Al? 

5. What do these mean? (a) H, Ho, 2H, 2O, O2, 2O2, CI, CI2, 
3CI, 3CI2; (b) N2, K, 2Ca, 3Fe, So, Cu, Alo. 

6. What is a formula? Illustrate. What does a single formula 
represent? 

7. State all that these mean. (a) H2O, 2H0O, KXO3. 4H0SO4, 
NaOH, NH4OH, CH3.OH, 3Ca(OH)2, Al2(S04)3, HNO3; (b) BaCl2.2HoO, 
2FeS, 3CaCl2, C12H22O11, 2ZnCl2, 3A1(0H)3, 4Ba(N03)2. 

8. Give from memory the formulas of the following compounds : 
water, potassium chlorate, sulphuric acid, magnesium oxide, copper oxide, 
sodium hydroxide. 

9. How many atoms of the different elements are in each formula 
in Exercise 7? 



SYMBOLS AND FORMULAS loi 

10. Define and illustrate molecular weight. How is it related to 
(a) a formula and (b) symbols? 

11. What is the molecular weight of each substance in Exercise 7? 

12. How does a formula express composition ? Illustrate by KNO3. 

13. State the steps in calculating the simplest formula of a com- 
pound. 

14. As in Exercise 13, in calculating percentage composition. 

PROBLEMS 

1. Calculate the molecular weight (or multimolecular weight) of 
the following compounds by finding the sum of the atomic weights : 

(a) magnesium oxide (]\IgO), (b) hydrogen peroxide, (c) zinc chlo- 
ride (ZnCl-i), (d) 2Cu(N03)2, (e) 3.^12(804)3, (/) potassium ferrocya- 
nide (K4Fe(CN)6), (g) 2Na2B407, {h) crystallized ferrous sulphate 
(FeS04.7H20). 

2. Calculate the simplest formula of the compounds which have 
the following percentage composition: (a) CI = 60.68, Xa = 39.31; 

(b) S = 23.52, Ca = 29.41, O = 47-05; (c) C = 40, H = 6.67, O = 

53-33- 

3. As in Problem 2: (a) N = 26.17, H = 7.48, Ci = 66.35; (b) As = 
75.8, O = 24.2; (c) N = 82.35, H = 17.65. 

4. As in Problem 2 : (a) Si = 19.5, C = 66.62, H = 13.88 ; (b) Ca = 
38.71, P = 20, O = 41.29; (;:) H = I, K = 39.06, C = 11.99, O = 

47-95- 

5. Calculate the formula of a compound 18 gm. of which contain 
8.4 gm. of iron and 9.6 gm. of sulphur. 

6. As in Problem 5: 0.84 gm. contain 0.587 gm. of iron and 0.253 
gm. of oxygen. 

7. Calculate the percentage composition of (a) hydrochloric acid, 
(b) hydrogen sulphide (H2S), (c) ammonia (XH3), (</) hydrogen peroxide. 

8. As in Problem 7 : (a) calcium oxide (CaO), (b) calcium carbonate 
(CaCOs), U) calcium sulphate (CaS04), (d) calcium fluoride (CaF2). 

9. As in Problem 7 • (a) cane sugar (C12H22O11) and (b) grape 
sugar (CeHriOe). 

10. As in Problem 7: (a) sodium phosphate (Xa3P04), (b) diso- 
dium phosphate (HXa2P04), (c) monosodium phosphate (H2XaP04), 
(d) phosphoric acid (H3PO4). 

11. Calculate the per cent of (a) copper and (b) water in crystallized 
copper sulphate (CUSO4.5H2O). 

12. Calculate the per cent of (a) F in SiF4, (6) Al in AIPO4, {c) O in 
Mn02, id) Pb in PbCOa- 



CHAPTER IX 

NITROGEN — THE AIR — ARGON AND HELIUM 
— LIQUID AIR 

110. Introduction. — Reference has already been made 
to the element nitrogen and its presence in the air. We 
have also learned a httle about the atmosphere — the 
great mass of gas that envelops the earth and extends 
several miles into space. The terms atmosphere, the air, 
and air are often used interchangeably ; though by the air 
or air we usually mean a Umited portion of the atmosphere, 
e.g. the air over a city, the air of a room, or a bottle of 
air. 

In Chapter II we studied oxygen, and learned among 
other things that this very active gas makes up about one 
fifth of the air. Since most of the remainder is nitro- 
gen, we shall study this element before considering the 
air. 

111. Occurrence of nitrogen. — The elementary gas 
nitrogen constitutes about four fifths (or exactly 78.122 
per cent) of the air. Nitrogen is a constituent of nitric 
acid (HNO3) and ammonia (NH3), and of important com- 
pounds related to them. Nitrogen is also found in many 
animal and vegetable substances essential to life, e.g. the 
compounds called proteins, which are indispensable in- 
gredients of our food and also of the muscles and nerves of 
our bodies. (See Chapter XXIV.) 

112. Preparation of nitrogen. — Nitrogen is prepared 
on a large scale from hquid air (129). It can also be ob- 



NITROGEN — THE AIR 



103 



taincd from air by removing the oxygen 
from air by phosphorus (Fig. 56). 

Phosphorus is put in a small dish or a cruci- 
ble cover supported on a cork floating in a 
vessel of water. Upon igniting the phos- 
phorus with a hot wire and placing a bell jar 
quickly over the cork, the phosphorus and oxy- 
gen unite, forming clouds of white phosphorus 
pentoxide (P2O5). This solid soon dissolves in 
the water, which rises inside the jar owing to 
the removal of the oxygen, and the nitro- 
gen is finally left. 




Fig. 56. — Prepara- 
tion of nitrogen 
by burning phos- 
phorus in confined 
air 



Nitrogen is prepared in the laboratory 
by heating a solution of sodium nitrite (NaNOo) and am- 
monium chloride (NH4CI). These two compounds form 
the unstable compound ammonium nitrite (XH4XO2) 
which decomposes into nitrogen (N2) and water (H2O) ; 
the gas is collected in bottles over water, just as in the 
case of oxygen and hydrogen. Small quantities of nitro- 
gen may be readily obtained by heating ammonium 
dichromate f(NH4)2Cro07) in a test tube. 

113. Properties of nitrogen. — Nitrogen is a colorless 
gas, and has no taste or odor. It is a little lighter than 
oxygen and air. A liter at standard conditions weighs 
1.25 gm. (A liter of oxygen weighs 1.43 gm. and one of air 
1.29 gm.) It is only slightly soluble in water. Subjected 
to a low temperature and increased pressure, nitrogen be- 
comes a colorless liquid and ultimately a white solid. 

114. Chemical conduct of nitrogen. — Nitrogen does not 
support combustion nor sustain Ufe. Flames are extin- 
guished by nitrogen and animals die in it, because the supply 
of ox>^gen is cut off. The fact that nitrogen quickly ex- 
tinguishes a candle flame and kills a mouse was first ob- 



I04 PRACTICAL CHEMISTRY 

served by Rutherford, a Scottish physician, who discovered 
the gas in 1772. Soon after, Lavoisier showed the true 
relation of nitrogen to the atmosphere ; and because the 
gas would not support life, he called the gas azote — a name 
now used by some French chemists. The name nitrogen 
was given to it because it is a constituent of the important 
compound niter {i.e. saltpeter, potassium nitrate, KNO3). 

Nitrogen is very much less active chemically than oxygen. 
Indeed, if we test it, as we did oxygen and hydrogen, we 
find that it responds to none of the common tests. It is 
sometimes called an inert element, because it does not com- 
bine with elements at ordinary temperatures. At high 
temperatures and under special conditions, how^ever, ni- 
trogen forms many compounds. It combines with mag- 
nesium and a few other metals at red heat, forming ni- 
trides, e.g. magnesium nitride (Mg3N2). Electric sparks 
cause nitrogen to combine with oxygen and with hydro- 
gen, forming nitrogen oxides and ammonia (NH3). Both 
these reactions, if hastened by a catalyst, proceed rapidly 
enough to enable us to convert nitrogen from the air into 
compounds needed as fertihzers and explosives (196, 197) . 

115. Uses of nitrogen. — Nitrogen on account of its 
inertness is used to fill some kinds of electric hght bulbs, 
and the stem of high-boiUng thermometers. It is also used 
in making ammonia, nitric acid, and a nitrogen fertilizer 
called calcium cyanamide (CaCN2). 

116. Nitrogen and life. — Nitrogen, as well as oxygen, 
is vitally connected with life, though in a different way. 
All animals need nitrogen for their growth. But although 
we live in an atmosphere containing such a large proportion 
of this gas, we cannot assimilate it directly. The nitrogen 
we inhale (along with the oxygen) is exhaled again unused. 
The nitrogen needed by animals must be eaten in the 



NITROGEN — THE AIR 



105 



form of nitrogenous food, such as lean meat, fish, wheat, 
and other grains. (See Protein, Chapter XXIV.) 

Nor have plants, with few exceptions, power to assimi- 
late free nitrogen from the atmosphere. Most plants take 
up combined nitrogen from the soil in the form of nitrates 
or of ammonia. Hence combined nitrogen is being con- 
stantly removed from the soil. In order to restore it, some 
nitrogen compound must be added, e.g. sodium nitrate 
(NaNOs), calcium nitrate (Ca(N03)2), ammonium chloride 
(NH4CI), ammonium sulphate ((NH4)2S04), or calcium 
cyanamide (CaCXo) ; organic 
materials are often used, e.g. 
manure, dried blood, and meat 
or fish scraps. A substance or 
mixture which restores nitro- 
gen (or some other chemical 
element like phosphorus or 
potassium) to the soil is called 
a fertilizer. 

Many experiments have 
shown, however, that legumi- 
nous plants, such as peas, 
beans, and clover, take up 
nitrogen from the air by means 
of bacteria, which are in nod- 
ules on their roots (Fig. 57). 
with a preparation which contains nitrogen-forming bacteria. 

117. Air is a mixture and not a compound. — Air is 
a mixture of several gases. Oxygen, nitrogen, and argon 
are the three ingredients that are always present in nearly 
constant proportions. Variable proportions of water va- 
por and carbon dioxide gas are always found, and also 
small quantities of compounds related to ammonia and 




Fig- 57- — A plant with nodules 
on the roots 

Sometimes soil is treated 



io6 PRACTICAL CHEMISTRY 

nitric acid. Near cities the air may contain considerable 
dust, sulphur compounds, and acids ; at the ocean some 
salt is often found. 

Hitherto we have dealt almost exclusively with com- 
pounds, and we have found that compounds have a constant 
composition, i.e. the constituents are united in a proportion 
which is always the same in the case of a given compound. 
Furthermore, we have seen that if we wish to make a com- 
pound, we must cause the elements to unite chemically, 
and conversely if we wish to decompose a compound we 
must tear the compound apart chemically. In a few words, 
chemical action is always concerned where compounds 
are formed or decomposed. Moreover, this action is usu- 
ally accompanied by heat changes. The following facts 
show that air is not a compound but a mixture of gases : — 

(i) The proportion of oxygen and of nitrogen is not fixed, 
but varies between small hmits. Therefore air does not 
have a constant composition and cannot be represented 
by a formula. 

(2) When nitrogen and oxygen are mixed in approxi- 
mately the proportions that form air, the product is iden- 
tical with air, but the act of mixing gives no evidence of 
chemical action. 

(3) When air is dissolved in water, a larger proportion 
of oxygen than nitrogen dissolves. If the oxygen and 
nitrogen were combined, the dissolved air would contain 
the same proportions of oxygen and nitrogen as air itself. 

(4) When air is liquefied and allowed to boil, the 
nitrogen boils off first (129). If air were a compound, 
liquid air would have a fixed boiling point. 

118. Proportions of the constant ingredients of air. — 
For many years it was beheved that pure air consisted 
solely of oxygen and nitrogen. But in 1894 it was found 



NITROGEN — THE AIR 



107 



that nearly 1.2 per cent (by volume) of the gas hitherto 
called nitrogen is argon (124). The normal proportions 
(by volume) of the constant ingredients of air are nitrogen 
78.122 per cent, oxygen 20.941 per cent, and argon 0.937 
per cent. These numbers are often stated approximately 
as oxygen 78, nitrogen 21, and argon 0.94. 

119. " Composition " of air. — Although air is a mixture, we 
usually speak of its '' composition." Samples of air from various 
parts of the globe show such a remarkable uniformity in the propor- 
tions of the constant ingredients that chemists 
have fallen into the habit of applying the term 
composition to air. 

The proportion of oxygen in the air can be found 
by several methods. In one, a known volum.e of 
air is shaken in a closed bottle with a mixture of 
pyrogallic acid and sodium hydroxide ; this so- 
lution absorbs the oxygen and leaves the nitrogen 
and argon unchanged. In another, a graduated 
glass tube, containing a known volume of air, is 
inverted in a jar of water, and a piece of phos- 
phorus attached to a wire is introduced into the tube 
(Fig. 58). The oxygen combines with the phos- 
phorus. In a few hours the phosphorus is removed, 
and the volume of residual gas is read. The dif- 
ference between the first and last volumes is oxy- 
gen. There is no simple way of separating the 
nitrogen and argon. 




Fig. 58. — Find- 
ing the per 
cent of oxygen 
in air by phos- 
phorus 



120. Water vapor in the air. — Water 
vapor is always present in air, owing to 
constant evaporation from the ocean 
and other bodies of water. When the temperature of the 
air falls sufficiently, the water vapor condenses and is de- 
posited in the form of dew, rain, fog, mist, frost, snow, 
sleet, or hail (67). The clouds are masses of minute drops 
of Uquid water formed by condensation of the water vapor 



io8 PRACTICAL CHEMISTRY 

in the cold upper air. The condensation of considerable 
moisture forms large drops, which fall to the earth as rain. 

The total amount of water vapor in the lower regions 
of the atmosphere is very large. However, the proportion 
in the air of different regions varies between wide limits. 
In rainy regions, such as tropical countries, it is large, 
while in desert countries it is small. 

A given volume of air absorbs a definite volume of water 
vapor and no more. Warm air holds more than cool air. 
Air containing its maximum amount of water vapor is said 
to be saturated at that temperature, or to contain loo per 
cent of water vapor. The saturation point is also called 
the dew point, i.e. the temperature at which it begins to 
deposit dew. On a pleasant day in a temperate climate 
the relative humidity, i.e. the relative amount of water 
vapor present, may vary from 30 to 90 per cent, the average 
being about 65 per cent. 

121. Test for moisture in the air. — The presence of water vapor 
in the air is shown by the moisture which collects on the outside of 
a vessel containing cold water, such as a pitcher of iced water. The 
moisture comes from the air around the vessel. For a similar reason, 
water pipes in a cellar and the cellar walls themselves are moist in 
summer. 

In the laboratory the presence of water vapor may be shown by 
exposing to the air a deliquescent substance, such as calcium chloride 
(86). If a known volume of air is drawn slowly through a weighed 
tube containing calcium chloride, the increase in weight gives the 
weight of water in the volume of air. 

The relative humidity may be calculated by first ascertaining the 
dew point and then comparing the final (dew point) pressure and the 
original (observed) pressure. For example, if air at 20° C. must be 
cooled to 12° C. before it deposits dew, its moisture content would be 
expressed as 10.48 mm. (73). If it were saturated at 20° C, its 
moisture content would have been equivalent to 17.41 mm. That 
is, its relative humidity was 10.48 -h 17.41, or 60.19 per cent. 



NITROGEN — THE AIR 109 

122. Physical comfort depends on water vapor in the 
air. — The proportion of water vapor in the air has a 
marked effect on our bodily comfort. When the relative 
humidity is near the average, we feel comfortable. But 
if the air is moist or dry we are very uncomfortable. 

The relation of water vapor to bodily comfort is simple. 
Our bodies have a normal and nearly constant temperature 
of 98.6° F. This temperature is maintained by the heat 
produced by the chemical changes in our bodies, espe- 
cially the oxidation of waste tissue by the ox\' gen carried 
by the blood to all parts of the body (27). But this tem- 
perature is regulated partly by radiation of heat and 
partly by evaporation of water from the surface of the 
body. Now if the air is moist, evaporation proceeds 
with difficulty ; whereas if the air is dry, it pro- 
ceeds too fast. In either case, we are uncomfortable, and 
try by various devices to increase our comfort. Thus, 
we use fans and w^ear thin clothing to promote evaporation, 
or we m.oisten the air by exposing pans of w^ater. 

Our comfort and efficiency depend on maintaining con- 
stant, moderate evaporation from the surface of the body. 
This desirable condition may be accomplished, or at least 
favored, by living in the open air as much as possible, main- 
taining the average humidity in our houses, wearing cloth- 
ing adapted to cUmatic conditions, and ventilating the 
rooms in which we live. 

123. Carbon dioxide in the air. — Carbon dioxide is one 
product of the breathing of animals, the combustion of 
fuels, and the decay of organic substances (33). By these 
processes vast quantities of carbon dioxide are being con- 
stantly introduced into the air. The proportion in ordinary- 
air is 3 to 4 parts in 10,000 parts of air, i.e. 0.03 to 0.04 per 
cent. In crowded rooms it is often as high as ^7, parts 



no 



PRACTICAL CHEMISTRY 



in 10,000. The proportion of carbon dioxide in the at- 
mosphere as a whole is practically constant, owing to winds 
and air currents, and largely, also, to the fact that this gas 
is absorbed by all green plants (39). 

The presence of carbon dioxide in air is detected by calcium hydrox- 
ide. If calcium hydroxide solution is exposed to air, the carbon diox- 
ide interacts with the calcium hydroxide, forming a thin, white crust 
of insoluble calcium carbonate on the surface of the Uquid. If con- 
siderable air is drawn through the calcium hydroxide solution, the 
liquid becomes milky, because the particles of calcium carbonate are 
suspended in the liquid (33 and Fig. 12). 

124. Argon in the air. — Argon, as stated above (118), 
is an essential and constant ingredient of the air, the pro- 
portion being 0.937 P^^ cent by volume. 

Argon is a colorless, odorless gas which is a httle heavier 
than oxygen. It dissolves in water to the extent of 

about 4 volumes in 100. 
It can be hquefied and 
solidified. 

A conspicuous property 
of argon is its lack of 
chemical activity. No 
compounds of this ele- 
ment have as yet been 
prepared or discovered. 
The name argon is hap- 
pily chosen, being derived 
from Greek words signi- 
fying inert. 

125. Discovery of ar- 
gon. — Argon was de- 
tected and first studied 
Fig. 59. - Ramsay (1852-1916) in 1894 by Rayleigh and 




NITROGEN — THE AIR iii 

Ramsay (Fig. 59). Rayleigh found that nitrogen ex- 
tracted from air had a greater weight than an equal 
volume of nitrogen obtained from compounds of nitrogen. 
Consequently, they beheved that the nitrogen from air 
contained another gas hitherto overlooked. Experiments 
(by Ramsay) showed that after the oxygen and nitrogen 
were removed from purified air, there still remained a 
small quantity of a new gas. It was named argon and 
given the symbol A. 

Argon was first obtained by Ramsay by passing pure air over heated 
copper to remove the oxygen, and then the remaining gas over heated 
magnesium or calcium to remove the nitrogen. He also passed elec- 
tric sparks through a mixture of air and oxygen, and absorbed the 
nitrogen oxides in potassium hydroxide solution. The latter method 
is a repetition of the one used by Cavendish in 1785 when he deter- 
mined the composition of air ; he observed and recorded the fact that 
a small bubble of gas always remained, which was doubtless argon. 
To Cavendish belongs the honor of first observing this element. 

A recent method of obtaining argon consists in liquefying air, and 
allowing the nitrogen and then the argon to boil off from the ox>'gen. 
This method is based on the fact that liquid argon boils at a higher 
temperature (-186° C.) than nitrogen ( — 195.7° C). 

126. Other gases in the atmosphere. — Helium, neon, krypton, 
and xenon are inert gases discovered by Ramsay subsequently to 
argon. With the exception of neon, they constitute an exceedingly 
minute proportion of the atmosphere. Like argon they do not form 
compounds. Ramsay estimated that in 1,000,000 parts of the atmos- 
phere there are 3 to 4 parts of helium, 10 to 20 of neon, 0.05 of krypton, 
and 0.006 of xenon. 

127. Helium was detected in the atmosphere of the 
sun by Lockyer in 1868. It was found by Ramsay, soon 
after he discovered argon, in the gases expelled from cer- 
tain rare minerals and in the gas and water of some min- 
eral springs. Helium is now obtained from natural gas 
which issues from the ground in certain parts of the United 



112 PRACTICAL CHEMISTRY 

States. By liquefying the gas, the helium can be sepa- 
rated from the other ingredients, owing to its low boiling 
point (—269° C). It is a Ught, non-inflammable gas. 
Both of these properties make hehum an excellent gas for 
filling balloons and hghter-than-air airships, and success- 
ful experiments have been made along this line. 

Helium is one of the disintegration products of radium (620) , 

128. What is liquid air? — Liquid air is a mixture of 
liquid oxygen and liquid nitrogen. It sometimes looks 
cloudy, owing to the presence of solid carbon dioxide and 
ice. When these soHds are removed by filtering, the fil- 
trate has a pale blue tint. 

129. Properties of liquid air. — If a beaker is filled with 
liquid air, the latter boils vigorously, the surrounding air 

becomes intensely cold, frost gathers on the 
beaker, and in a short time the liquid air 
will disappear into the air of the room. 
If, however, Hquid air is put into a Dewar 
flask, evaporation takes place so slowly 
that some liquid air will remain in the flask 
several days. 

A Dewar flask (Fig. 60) consists of two flasks, 

one within the other sealed together air-tight at 

Fig. 60. — A ^Yie top ; the space between the flasks is a vacuum. 

e\\ ar as ^j^^ surfaces of the flasks are coated with silver, which 

reflects heat and helps retard the evaporation of the liquid air. Liquid 

air is stored and transported in Dewar flasks. 

Liquid air boils at about —190° C. If it is allowed to 
boil in a proper apparatus, the nitrogen (boiling point 
— 195.7° C.) escapes first, leaving more or less pure oxygen 
(boiling point —182.9° C). (See also 125.) The industrial 
separation is accomplished this way, the two gases being 
collected in separate tanks. 




NITROGEN — THE AIR 113 

130. Some experiments with liquid air. — A tin or iron 

vessel which has been cooled by hquid air is so brittle that 
it may often be crushed with the fingers ; while a piece 
of rubber tubing becomes as brittle as glass. Mercury 
freezes so hard in liquid air that it can be used as a hammer 
to drive a nail. 

When liquid air is poured into a kettle standing on 
a block of ice, the hquid air boils vigorously because 
the ice is so much ^' hotter." If a kettle of liquid air is 
placed over a hghted Bunsen burner, frost and ice collect 
on the bottom of the kettle, because the intense cold pro- 
duced by the evaporation of the liquid air in the kettle 
solidifies the water vapor and carbon dioxide, which are 
the tw^o main products of burning illuminating gas. If wa- 
ter is now poured into the kettle, the hquid air boils over 
and the water is instantly frozen ; the water is so much 
" hotter " than the liquid air that the latter boils more 
violently, and since its rapid evaporation causes the ab- 
sorption of heat, the water loses heat and becomes ice. 
■ Ordinary liquid air is from one half to one fifth hquid 
oxygen, and will support combustion. A glowing stick 
or a red-hot rod of steel burns brilliantly in this cold hquid. 

131. Manufacture of liquid air. — Liquid air is manufactured by 
forcing air cooled by water through a pipe to a valve. As it escapes 
through the valve, it expands and its temperature falls, because 
expansion is a cooling process. After expansion, the cold air is led 
back over the outer surface of the same pipe by which it came, where- 
upon it rapidly regains its former temperature. But in so doing it 
cools the pipe itself and the air within it. This latter air in turn 
expands and falls in temperature, but as it was colder than the first 
portion before expansion, so it is colder after expansion. Since the 
pressure within the pipe is maintained by a continuous supply of air 
under pressure, the pipe becomes continually colder, until finally the 
expanding air at the valve liquefies in part. 



114 PR-\CTIC-\L CHEMISTRY 

EXERCISES 

1. How ii nitrogen prepared? :?ummarize its properties. Com- 
pare the chemical conduct of nitrogen and oxygen. For what is nitro- 
gen used? 

2. What is the relation of nitrogen to the life of (a) animals and 
(6) plants? 

3. What are the two chief ingredients of the atmosphere? The 
constant ingredients? The variable ingredients? The ingredients 
found in traces? What special substances are sometimes found in 
the air of cities ? 

4. State the volumetric composition of air. How is it found? 

5. Has air a chemical formula? If so, what is it? If not, why? 

6. Describe the action of air upon (a) calcium hydroxide and 

(b) calcium chloride. 

7. What is the meaning of the term de-u- paint? Relaihe humidity ? 

8. Discuss the relation of physical comfort to water vapor in air. 

9. Give several proofs that air is a mixture. 

10. What is argon? Give a brief account of (a) its discovery, 
(6) its prop>erties. (c) its method of preparation. What proportion 
of air is argon ? What is the significance of the name argon ? 

11. What is liquid air? What are its chief properties? Describe 
a Dewar flask. 

12. Topics for home study: (a) Helium, (h) Uses of nitrogen. 
ic) Function of oxj-gen in the air . (d) Atmospheric pressure, (ei Ven- 
tilation, (f) Carbon dioxide in the air. ig) Lavoisier and combustion. 
(A) Cavendish and air. 

13. Practical topics: (a) How would you distinguish nitrogen 
from carbon dioxide ? (6) Why are mines and cellars damp ? (c) Why 
does the composition of the atmosphere var>- so slightly? (d) How 
can the relative humidity of a room be increased in a heated house ? 

(c) Of what advantage is helium in a balloon ? 

PROBLEMS 

1. What is the weight of air in a room 6 X 8 X 5 m. ? !'A liter 
of air weighs 1.29 gm.) 

2. How many kilograms of pure air are needed to yield [a) 100 kg. 
and (h) 100 1. of oxygen (at standard conditions) ? 

3. Express in inches the following barometer readings : (a) 760 mm., 
(6) 745 mm., (c) 70 cm., (d) 0.769 m., (e) 7.49 dm., (/) 780 mm., (g) 5 mm. 

4. What is the weight at 0° C. and 760 mm. of {a) 1000 cc. of dry 
air? Of {h) 95 L, (c) 95 cc, {d) 95 cu. m.? 



I 



CIL\PTER X 
CHEMICAL REACTIONS — EQUATIONS — CALCULATIONS 

132. Chemical reactions. — The substances that par- 
ticipate in a chemical change are said to undergo chemical 
action, to interact, or to react. A single chemical change is 
called a chemical reaction, an interaction, or simply a re- 
action. 

133. What is a chemical equation? — We learned in 
14 that a reaction can be represented in a condensed form 
called an equation. Thus : — 

Iron -f Sulphur = Iron Sulphide 

In the preceding chapters certain chemical changes were 
represented by equations. In 105. 106 we found that ele- 
ments and compounds are represented by s\Tnbols and 
formulas. Therefore, we can now remodel the prelimi- 
nan' equations into chemical equations by using sjinbols 
and formulas in place of words. The above equation then 

becomes : — 

Fe — S = FeS 

134. How to write an equation. — The mere change of 
words to symbols and fonnulas would not always give a 
correct equation. In order to write the equation that 
correctly expresses a chemical change, we must know cer- 
tain facts and express them in the correct chemical way. 
Thus, we must know the symbols and formulas of the factors 
(the reacting substances') and of the products (the hnal 
substances'). Next we must \sTite a preliminan- equation. 



ii6 PRACTICAL CHEMISTRY 

and then adjust it so that there is the same number of atoms 
of each element on both sides of the final equation. 

These are the steps in writing an equation: (i) Write 
on the left (of the equality sign) the symbol or formula 
of each factor. (2) Write on the right the symbol or for- 
mula of each product. (3) Balance the preliminary equa- 
tion, if necessary. 

To balance an equation we increase the number of atoms, 
or molecules, or both — as necessary — until the number 
of atoms of each element (free or combined) is the same 
on both sides of the equation. Let us take three examples. 

First, when magnesium and oxygen form magnesium 
oxide, the preliminary equation is : — 

Mg + O2 = MgO 

Inspection shows that there are 2 atoms of oxygen (in O2) 
on the left but only i (in MgO) on the right. Hence we 
must increase the number of oxygen atoms on the right. 
We do this by prefixing the coefficient 2 to the formula 
MgO (not by altering the MgO). This change necessitates 
multiplying Mg on the left by 2. The final balanced equa- 
tion then becomes : — 

2Mg + 02 = 2MgO 

Final inspection shows that the same number of atoms of 
each element is on both sides of the equation, hence the 
equation is correct. 

Second, when zinc and hydrochloric acid interact, hy- 
drogen and zinc chloride are formed. The preliminary 
equation is: — 

Zn -f HCl = H2 + ZnCl2 

By inspection it is evident that 2 atoms of chlorine (in ZnCl2) 
are on the right and only i is on the left. Hence we m.ust 



CHEMICAL REACTIONS — EQUATIONS 1 1 7 

multiply HCl by 2, thereby providing 2 atoms of chlorine, 
and giving also the 2 atoms of hydrogen. The final bal- 
anced equation becomes : — 

Zn + 2HCI = H2 + ZnCl2 

Third, when potassium chlorate is decomposed, oxygen 
and potassium chloride are produced. The preliminary 
equation is : — 

KCIO3 = 02 + KCl 

By inspection we see that there are 3 atoms of oxy^gen (in 
KCIO3) on the left but only 2 (in Oo) on the right. To 
obtain the same number on each side, we must multiply 
KCIO3 by 2 and O2 by 3. The second preliminary equation 
is : — 

2KCIO3 = 3O2 + KCl 

Inspecting again, it is clear that there are 2K and 2CI 
on the left but only i each on the right. Therefore, we 
balance by multiplying KCl by 2, and obtain the final cor- 
rect equation : — 

2KCIO3 = 3O2 + 2KCI 

135. Some precautions to be observed in writing equa- 
tions. — (a) Correct formulas must be used. If a formula 
is not remembered or is not given in the immediate text, 
it should be looked up in the book ; this can be done by 
finding the name of the substance in the index and con- 
sulting the proper page where, as a rule, the formula is 
given. Thus, when sodium interacts with water, sodium 
hydroxide and hydrogen are formed. By referring to the 
page in the text under which sodium hydroxide is indexed. 



ii8 PRACTICAL CHEMISTRY 

we find its formula is NaOH. The preliminary and final 
equations are : — 

Na + HoO = NaOH + Ho 
2Na + 2H2O = 2NaOH + H2 

(b) It must not be overlooked that the correct formulas of 
many elementary ga5g5, such as oxygen, hydrogen, nitrogen, 
and chlorine, are O2, H2, N2, CI2 respectively (not O, H, etc.). 

(c) In balancing an equation these rules are helpful : 
(i) Start with the formula containing the most atoms of one 
element. (2) Find the other formula (or symbol) containing 
this element, and increase the number of atoms of this 
element by prefixing a coefficient, not by altering the for- 
mula (or symbol) — see middle of page 116. (3) Increase 
again, if necessary. (4) Balance in the same way for the 
other elements. (5) Check up, so that finally the total num- 
ber of atoms of each element is the same on both sides. 
Let us take an example. When phosphorus burns in oxy- 
gen, phosphorus pentoxide is formed. The formula of 
phosphorus pentoxide is P2O5. Hence the prehminary 
equation is : — 

P + O2 = P2O5 
By inspection we see that P2O5 needs at least 5 atoms of 
oxygen. Clearly the only way to balance the equation 
for oxygen is to multiply O2 by 5 and P2O5 by 2 ; this ad- 
justment gives 10 atoms of oxygen on each side, thus : — 

P -f 5O2 = 2P2O5 
But multiplying P0O5 by 2 gives 4 atoms of P on the right, 
because a coefficient multipHes the whole formula. That 
is, 2P2O5 means two molecules each containing 2P and 5O. 
Hence we balance for P by multiplying P on the left by 4. 
The final equation then becomes : — 

4P + 5O2 = 2P2O5 



CHEMICAL REACTIONS — EQUATIONS 119 

(d) Only the substances that actually take part in the 
chemical change should be included in the equation. Thus, 
when magnesium is burned in air, the nitrogen of the air 
does not unite with the magnesium (to any extent). Hence 
nitrogen does not appear in the equation. Similarly in 
the equation for the preparation of hydrogen from zinc 
and hydrochloric acid, no water (H2O) appears as a factor 
because the water (in the dilute sulphuric acid) does not 
participate in the reaction. 

(e) The terms of an equation, i.e. symbols and for- 
mulas, cannot be transposed as in the case of an algebraic 
equation. A chemical equation is the expression of an 
actual chemical change ; it is the outcome of an experi- 
ment. A chemical equation, although it contains the plus 
sign, has none of the properties of an algebraic equation 
except equality of the total weights on each side. 

136. How to read an equation. — The plus ( + ) sign 
may be read and or plus and the equality ( = ) sign fonn(s), 
gives{s), or equal{s). An arrow ( — >■) is sometimes used 
instead of the equality sign ( = ) ; both signs are read in the 
same way. Since equations are really expressions of equal- 
ity between two total weights, there is a good reason for 
using the sign of equality. (Compare 174.) 

Consider the equation : — 

Zn + H2SO4 = H.2 + ZnS04 

This equation may be read in several ways: (i) zinc and 
sulphuric acid form (or give) hydrogen and zinc sulphate ; 
(2) zinc plus sulphuric acid equal hydrogen plus zinc sul- 
phate ; (3) one atom of zinc and one molecule of sulphuric 
acid form one molecule of hydrogen and one molecule of 
zinc sulphate. (A fourth way is given in 208.) 



I20 PRACTICAL CHEMISTRY 

137. Ordinary equations have a limited meaning. — The equa- 
tions we are studying in this chapter might be called ordinary equa- 
tions or atomic equations. They merely show the result of a reaction 
by the proper number of atoms and molecules. Other kinds of equa- 
tions are used to tell other facts about chemical change, and these 
will be discussed in the proper places. 

Ordinary equations show nothing about the physical conditions 
under which a reaction occurs. Thus, the equation 

2Mg +02= 2MgO 

does not show that the reaction takes place quickly at a moderate 
temperature {e.g. heat from a burning match). Nor does the equation 

2HgO = 2Hg + O2 

show that the reaction takes place rather slowly and only by con- 
stant heating at a high temperature {e.g. heat from a Bunsen burner). 
So also ordinary equations do not include the solvent, although 
many reactions occur only in solution. Moreover, ordinary equa- 
tions tell nothing about the way in which a reaction occurs. Thus, in 
the equation 

2KCIO3 = 3O2 + 2KCI 

several chemical changes doubtless occur which do not appear in the 
equation. The main purpose of this equation is to express in the 
simplest way the transformation of potassium chlorate into the two 
products oxygen and potassium chloride. 

138. Ordinary equations are gravimetric equations.— 

Ordinary equations, in spite of certain limitations, have 
a practical use which is very important. 

We have seen so far that equations show in a compact 
way the products formed by the reaction of certain sub- 
stances and that they also show the number of mole- 
cules (and in some cases the atoms) of each substance in- 
volved in a reaction. Thus, the equation 

4H2O + 3Fe = Fe304 + 4H2 



CHEMICAL REACTIONS — EQUATIONS 121 

not only shows that iron oxide and hydrogen are the prod- 
ucts of the interaction of water (in the form of steam) 
and iron, but also that 4 molecules of water and 3 atoms 
of iron interact to form i molecule of iron oxide and 
4 molecules of hydrogen. 

Equations are quantitative expressions. They are based 
on the fact that a chemical change conforms to the law of 
the conservation of matter, viz., No matter is lost or gamed 
in a chemical change. We start with a certain total weight 
and we have the same total weight at the end of the re- 
action. This is only another way of saying that we have 
the same number of atoms on each side of a balanced equa- 
tion, because we have the same sum of atomic weights on 
each side of the equation. Indeed, there could be no 
" equation " unless both sides were equal in weight. 
Briefly, ordinary equations are gravimetric. 

139. Calculations based on equations. — Each atom 
stands for a certain weight. Hence we can wTite the equa- 
tion for the interaction of zinc and sulphuric acid thus : — 

Zn + H2SO4 = H2 + ZnS04 

65 2 + 32+64 2 65+32+64 

65 98 2 161 

The equation in this form is read : 65 parts by weight of 
zinc plus 98 parts by weight of sulphuric acid equal 2 parts 
by weight of hydrogen and 161 parts by weight of zinc 
sulphate. That is, these numbers are the relative weights 
of the different substances involved in this reaction. Zinc 
and sulphuric acid always interact in the ratio of 65 to 
98 and produce hydrogen and zinc sulphate in the ratio 
of 2 to 161. 

In actual practice, of course, we do not have to start 
with exactly 65 gm. of zinc or with 98 gm. of sulphuric acid. 



122 PRACTICAL CHEMISTRY 

We can use any convenient \yeights ; but whatever weights 
we use, these two substances interact in the ratio of 65 
to 98 and the quantity of either substance greater than 
the amount for the required ratio will be left unchanged. 

Suppose we start with 45 gm. of zinc, pour sulphuric acid 
upon it, and let the reaction continue until the zinc is used 
up. We can calculate readily the weight of the sulphuric 
acid used. 

First, we write the equation. Thus : — 

Zn + H0SO4 = Ho + ZnS04 

Second, we place under each term of the equation its 
correct relative weight, i.e. the weight for which the com- 
plete symbol or formula stands, using for this purpose the 
approximate atomic weights in the table on the back in- 
side cover. Thus : — 

Zn + H2SO4 = Ho -f ZnS04 

65 2 + 32 -f- 64 2 65 -f- 32 + 64 
65 98 2 161 

Third, we place above the symbol for zinc the given 
weight, which is 45 in this example, and above the for- 
mula for sulphuric acid the letter x to denote the required 
weight. Thus : — 

45 ^ 

Zn -f- H0SO4 = Ho -t- ZnS04 

65 98 2 161 

Fourth, we state in a proportion the four quantities in- 
volved. In this proportion the equation weights (below 
the equation) are the first and second terms, while the 
corresponding known and required weights (above the 
equation) are the other two terms. Thus : — 

65 : 98 : : 45 : a; 



CHEMICAL REACTIONS — EQUATIONS 123 

Fifth, we iinally solve the proportion for x, remembering 
that the product of the means (the two inner terms) equals 
the product of the extremes (the two outer terms) . Thus : — 

98 X 45 = 65 X A- .-. X = ^}^AS^ 01- 5^ g ^^^^ 5^ 3 „^ 

The quantity of each product can be found by a similar 
proportion. 

Another example will make the process clearer. This 
time we start with 15 gm. of potassium chlorate and wish 
to know the weight of oxygen which can be obtained. Pro- 
ceeding as above, we have these steps : — 

(i) Chemical equation: — 

2KCIO3 = 3O2 + 2KCI 

(2) Relative weight equation : — 

2KCIO3 = 3O2 + 2KCI 

2(39 + 35-5+48) 3(32) 2(39 + 35.5) 
2(122.5) 96 2(74.5) 

245 96 149 

(3) Reacting weight equation : — 

15 X 

2KCIO3 = 3O2 + 2KCI 
245 96 149 

(4) Proportion : — 

245:96:: 15:0; 

(5) Solution : — 

96 X 15 = 245 X X :. X = 96_X_15^ ^^ ^ g^^ ^^^^ ^ g^ gni^ 

245 
140. Calculations involving weight and volume. — Cal- 
culations like those in 139 are limited to weights — gravi- 



124 PRACTICAL CHEMISTRY 

metric calculations. But many reactions involve gases, 
and it is often necessary to know the volume of the gas as 
well as its weight. To calculate the volume, we calculate 
the weight in the usual way and then convert the weight 
into volume ; or vice versa. 

Let us take two examples. First, suppose we wish to 
know the volume of hydrogen liberated by the interaction 
of 20 gm. of zinc and sufficient dilute sulphuric acid. Pro- 
ceeding as in 139, we have : — 



(l) 




Zn + H2SO4 


= Ho + ZnS04 


(2) 




Zn + H2SO4 
65 98 


= H2 + ZnS04 
2 161 


(3) 




20 

Zn + H2SO4 

65 98 


X 

= H2 + ZnS04 
2 161 


(4) 




65:2:: 


20: X 


(5) 


2 X 


20 = 65 X X : 


•-^^/% 



, or 0.61 S- 

Then 

(6) Since i liter of hydrogen weighs 0.09 gm. (52), the 
volume of hydrogen is : — 

^^^= 6.83. Ans. 6.83 1. 
0.09 

As a second example, suppose we wish to know the weight 
of calcium carbonate needed to produce 200 liters of car- 
bon dioxide. First, we find the weight of 200 Hters of car- 
bon dioxide. Since i hter weighs 1.98 gm. (36 and Ap- 
pendix, § 3), the weight of 200 hters is 200 X 1.98, or 396 
grams. Proceeding as above we have : — 

(i) CaCOa + 2HCI = CO2 + CaCl2 + H2O 



CHEMICAL REACTIONS — EQUATIONS 125 



(2) CaCOs -f 2HCI = CO2 + CaClo + HoO 
40+12+48 2(1+35.5) 12+32 40 + 71 2 + 16 



100 

(3) ^ 
CaCOa 
100 



73 



44 
396 



III 



+ 2HCI = CO.2 + CaClo + HiO 



(4) 
(5) 



73 

100 : 44 



44 
X : 396 



III 



44 X X = 100 X 396 .-. X = ^^, or goo. 

44 



Ans. 900 grams. 

141. Equations for preceding reactions. — The equations cor- 
responding to many reactions already discussed may be collected 
here, partly for review and partly for use in solving problems. 







2HgO 
Mercuric Oxide 


O2 
Oxygen 


+ 


2Hg 

Mercury 




2KCIO3 
Potassium Chlo-ate 


3O2 
Oxygen 


+ 2KCI 
Potassium Chloride 






2Pb02 

Lead Dioxide 


O2 
Oxygen 


+ 


2PbO 
Lead Oxide 






2Ba02 
Barium Dioxide 


O2 

Oxygen 


+ 


2BaO 
Barium Oxide 






2H.2O 
Water 


2 Ho 
Hydrogen 


+ 


0,> 
Oxygen 


s 

Sulphur 


+ 


O2 
Oxygen 


SO2 
Sulphur Dioxide 




C 

Carbon 


+ 


O2 
Oxygen 


CO2 
Carbon Dioxide 




2CU 

Copper 


+ 


O2 
Oxygen 


2CuO 
Copper Oxide 






Zn 
Zinc 


+ 


H2SO4 
Sulphuric Acid 


II.. 
Hydrogen 


+ 


ZnS04 

Zinc Sulphate 



126 



PRACTICAL CHEMISTRY 



Zn 

Zinc 



+ 2HCI 

Hydrochloric 
Acid 



H2 + ZnCls 

Hydrogen Zinc Chloride 



2Na + 

Sodium 



2H2O 
Water 



H2 
Hydrogen 



+ 2XaOH 
Sodium Hydroxide 



Ca 

Calcium 



2H2O 
Water 



H2 

Hydrogen 



+ Ca(0H)2 
Hydroxide 
Calcium 



2AI + 6XaOH = Ho 

Aluminium Sodium Hydroxide Hydrogen 



+ 2Xa3A103 
Sodium Aluminate 



2H2 + O2 

Hydrogen Oxygen 



2H2O 

Water 



CuO + Ho 

Copper Oxide Hydrogen 

NaCl + AgNOs 

Sodium Silver 

Chloride Nitrate 



H2O 
Water 

AgCl 

Silver 

Chloride 



+ 



Cu 

Copper 



+ NaNOs 
Sodium 
Nitrate 



EXERCISES 

1. Prepare a summary of 132 to 138. 

2. Define and illustrate the terms reaction and equation. 

3. State (a) the three steps in writing an equation, and {h) the 
rules for balancing an equation. 

4. What precautions must be observed in writing equations? 

5. Select an equation from 141 and read it in three different ways. 

6. Interpret the equation 2Cu + Oo = 2CuO by stating {a) what 
it means and {h) what it does not include or express. 

7. Write equations for the following reactions : (a) Calcium and 
hydrochloric acid form calcium chloride and hydrogen, {h) Potas- 
sium sulphate and barium chloride form barium sulphate and potassium 
chloride, (c) Calcium carbonate and hydrochloric acid form calcium 
chloride, water, and carbon dioxide. 

8. As in Exercise 7 : (a) Calcium oxide and carbon dioxide form 
calcium carbonate, {h) Chlorine and aluminium form aluminium tri- 
chloride, (c) Carbon and lead oxide (PbO) form lead and carbon mon- 
oxide. 



CHEMICAL REACTIONS — EQUATIONS 127 

9. What is a gravimetric equation? Illustrate. 

10. Balance these equations : (a) BaCl2 + H2SO4 = BaS04 + 
HCl; (h) Pb(N03)2 + H2S = PbS + HNO3 ; (c) AICI3 + NH4OH = 
A1(0H)3 + NH4CI; (d) NaOH + CO2 = Na2C03 + H2O. 

11. Balance these equations: (a) Zn + HNO3 = H2 + Zn(X03)2; 
(b) HCl + ZnO = ZnCl2 + H2O ; (c) H2SO4 + NaNOa = Na2S04 + 
HNO3; (d) SO2 + O2 = SO3. 

12. State in order the steps in calculating the weight of a substance 
when the weight of only one reacting substance is given (139). 



PROBLEMS 

1. How many grams of oxygen can be prepared from (a) 45 gm. of 
mercuric oxide, {b) i kg. of potassium chlorate, (<:) 1000 gm. of water? 

2. As in Problem 1, from (a) 750 gm. of lead oxide (PbOa), 
(b) 2200 gm. of barium dioxide (Ba02)? 

3. Hydrogen is prepared from sulphuric acid and 40 gm. of zinc. 
Calculate the weights of the products of the reaction. 

4. If a balloon holds 150 kg. of hydrogen, how much (a) zinc and 

(b) sulphuric acid are needed to generate the gas? 

5. What volum.e of oxygen at standard conditions could be ob- 
tained from 10 gm. of potassium chlorate? 

6. If 10 gm. of pure carbon are burned in air, what weights of other 
substances are involved? 

7. One gram of copper is heated intensely in air, and the product 
is reduced by a gas. Calculate (a) the weights of the other substances 
involved in the two reactions, and (b) the volume of the gas in the 
second reaction. 

8. How many grams of potassium chlorate are needed to prepare 
(a) 100 gm. of oxygen and (b) 100 1. (at standard conditions)? 

9. Calculate the weights needed in the following reactions : 
(a) water and 100 milligrams of sodium, (b) calcium and 100 milligrams 
of water, (c) sodium hydroxide and 25 gm. of aluminium. 

10. What weight of carbon dioxide is formed by burning a ton of 
coal which is 90 per cent carbon? 

11. Suppose 85 gm. of water are decomposed. What (a) weights 
and (6) volumes of gases are produced? 

12. Sixty grams of mercuric oxide are decomposed. What volume 
of oxygen at 91° C. and 380 mm. is produced? 

13. How much water can be obtained from (a) 34 gm. of crystallized 
zinc sulphate (ZnS04.7H20), (b) 1000 kg. of selenite (CaS04.2H20), 

(c) 1000 gm.. of washing soda crystals (Na2C03.ioH20)? 



128 PRACTICAL CHEMISTRY 

14. Write the equation for the interaction of barium nitrate and 
sodium sulphate. If 170 gm. of barium nitrate are used, calculate the 
weights of the other compounds involved. 

15. Ammonia and hydrogen chloride form solid ammonium chloride. 
Write the equation for this reaction. If 210 gm. of ammonia are used, 
calculate (a) the weights of the other compounds involved, and (b) the 
volumes of ammonia and hydrogen chloride needed. 

16. The oxygen is liberated from 10 gm. of potassium chlorate, and 
ID gm. of sulphur are burned in the gas. How much sulphur, if any, 
is left? 



I 



CHAPTER XI 



CHLORINE - HYDROGEN CHLORIDE— HYDROCHLORIC ACID 



.^^fl 



142. Introduction. — So far we have studied the ele- 
ments oxygen, carbon, hydrogen, and nitrogen, the com- 
pounds carbon dioxide, carbon monoxide, and water, and 
the mixture air. In this chapter we shall study the element 
chlorine and its common compound hydrogen chloride. 

143. Occurrence of chlorine. — Free chlorine is never 
found in nature, but its compounds, especially chlorides, 
are widely distributed, the most abundant being sodium 
chloride (NaCl) or common salt. Many compounds of 
chlorine with potassium, magnesium, 
and calcium are found in the deposits 
at Stassfurt in Germany. (See Potas- 
sium, Chapter XXIX.) Sea water 
contains sodium and magnesium chlo- 
rides. 

144. Preparation of chlorine. — 
Chlorine is prepared on a large scale 
by the electrolysis of a solution of 
sodium chloride. When an electric 
current is passed through a solution 
of sodium, chloride, chlorine gas is 
liberated in one compartment of the 
apparatus and sodium hydroxide is formed in the other. 
The chlorine is conducted off through pipes, and the dis- 
solved sodium hydroxide is drawn off at intervals. This 
process is further described in 456. 

129 




Fig. 61. — Apparatus 
to illustrate the prep- 
aration of chlorine 
by the electrolysis of 
a solution of sodium 
chloride. 



I30 



PRACTICAL CHEMISTRY 



This process can be readily demonstrated. The apparatus is 
shown in Fig. 6r. A solution of sodium chloride is put in the battery 
jar .4 ; a little litmus solution is added and then enough dilute hydro- 
chloric acid to color the solution a distinct red. A block {B) divides 
the jar into two compartments (C and D), and the two pieces of elec- 
tric light carbon serve as electrodes {E and F). Soon after the cur- 
rent (from four or more cells or from a reduced street current) is 
turned on, the solution is bleached by the liberated chlorine in one 
compartment and turned blue by the sodium hydroxide in the other. 
The chlorine can also be detected by its odor. 

Chlorine is prepared in the laboratory by heating con- 
centrated hydrochloric acid with manganese dioxide. The 
equation is : — 

4HCI + Mn02 = CI2 + MnClo + 2H2O 



Hydrochloric 
Acid 



Manganese 
Dioxide 



Chlorine 



Manganese 
Bichloride 



Water 



A simple form of laboratory appara- 
tus is shown in Fig. 62. The manga- 
nese dioxide is put into the flask A 
and concentrated hydrochloric acid is 
introduced through the dropping tube 
B. By gently heating the flask, chlo- 
rine passes to the bottom of the bottle 
G and displaces the air. 

145. Properties of chlorine. — 

Chlorine is a greenish yellow 
gas. Its color suggested the 
name chlorine (from the Greek 
word chloros, meaning greenish 
yellow), which was given to it by 
paring chlorine in the lab- Davy about 1810. It has a dis- 
oratory agreeable odor, which is very pen- 

etrating. If breathed, it irritates the sensitive lining of the 
nose and throat ; a large quantity produces lung trouble, 
and would ultimately cause death. Chlorine was the first 




Fig. 62. — Apparatus for pre- 



CHLORINE — HYDROGEN CHLORIDE 



131 



poison gas used in the World War. It is about 2.5 times 
as heavy as air. Hence it is easily collected by downward 
displacement, i.e. by conducting it downward to the bot- 
tom of a vessel and allowing it to displace the air. A 
liter of dry chlorine at 0° C. and 760 mm. weighs 3.22 gm. 




Fig. 63. — Interior of a plant for liquefying and sioring chiorme. 
Cylinders full of chlorine are in the foreground 

Chlorine can be readily liquefied and solidified. Liquid 
chlorine is sold in strong iron cylinders (Fig. 63 and ?lso 

Fig. 3S)- 

146. Chlorine dissolves in water. — The solution of 
chlorine is yellowish, and smells strongly of chlorine. 
Chlorine water, as the solution is called, is unstable. If 
the solution is placed in the sunhght, oxygen is slowly 
liberated and can be collected in a suitable apparatus, e.g. 
a long tube (87 and Fig. 46). 

The oxygen does not come directly from the water but from a 
compound called hypochlorous acid (HCIO), which is formed in small 
quantities in the solution ; some hydrochloric acid is also formed. 
The reaction may be represented thus : — 



132 PRACTICAL CHEMISTRY 

CI2 -f H2O = HCIO + HCl 

Chlorine Water Hypochlorous Acid Hydrochloric Acid 

The hypochlorous acid is unstable and decomposes, thus : — 

2HCIO = Oo + 2HCI 

The reactions continue until all the chlorine is used up ; the equation 
for the completed change is : — 



2HOO 


+ 


2CU 


4HCI + 


0, 


Water 




Chlorine 


Hydrochloric Acid 


Ox>'gen 



147. Chemical conduct of chlorine. — Chlorine is a 
very active element. It unites vigorously with many 
elements at ordinary temperatures. Thus, if sodium, 
iron, copper, or other metals are merely warmed and then 
put into chlorine, they unite with the chlorine at once ; 
the sodium produces a dazzling light, and the copper and 
iron glow and emit dense fumes. These chemical changes 
illustrate the broad use of the term combustion. (See 53.) 
The compound formed in each case is a chloride, i.e. a com- 
pound of chlorine and one other element, e.g. sodium chlo- 
ride (NaCl) and iron chloride, (FeCls). 

Chlorine combines readily with hydrogen (53). The 
equation for this reaction is : — 

H2 + CI2 = 2HCI 

Hydrogen Chlorine Hydrogen Chloride 

A jet of burning hydrogen when lowered into chlorine 
continues to burn, forming a colorless gas called hydrogen 
chloride ; the latter becomes a white cloud when the breath 
is blown gently across the mouth of the vessel (155). 

The tendency of chlorine to combine with hydrogen is so great 
that the hydrogen of many compounds is withdrawn chemically by 
chlorine. Thus, when cotton saturated with hot turpentine (CioHig) 
is put into chlorine, white fumes, due to the formation of hydrogen 



CHLORINE — HYDROGEN CHLORIDE 133 

chloride, appear almost at once ; soon the chemical change is so vig- 
orous that a flame is produced. Since carbon does not unite directly 
with chlorine, the white fumes of hydrogen chloride are finally ob- 
scured by a dense cloud of black smoke. 

148. Chlorine bleaches. - Chlorine changes many col- 
ored substances into colorless ones. For example, colored 
cloth, whether dyed or naturally colored by impure sub- 
stances, is whitened {i.e. bleached) by moist chlorine. Dry 
chlorine does not bleach. 

149. Sources of chlorine for bleaching. — Chlorine 
water, prepared by bubbling chlorine through cold water, 
is sometimes used as a bleaching agent. The commonest 
source, however, is bleaching powder (CaOClo) or, as it 
is often called, chloride of lime. It is a yellowish white 
substance which smells like chlorine, but the smell is really 
due to hypochlorous acid. 

Bleaching powxler is manufactured by treating slaked lime 
(Ca(OH)o) with chlorine, the equation for the reaction being : — 



Ca(OH)o + 


Clo 


CaOCl, + 


H,0 


Calcium Hydroxide 


Chlorine 


Bleaching Powder 


Water 



If bleaching powder is treated wdth an acid, chlorine is 
liberated, thus : — 



CaOCI, 


+ H0SO4 = 


= Clo -f CaS04 + 


HoO 


Bleaching 


Sulphuric 


Chlorine Calcium 


Water 


Powder 


Acid 


Sulphate 





These reactions also take place : — 

CU + HoO = HCIO -f HCl 
HCIO = HCl + O 

The bleaching action is really due to the liberated oxygen, 
which in this equation is represented by O, rather than 
O2. The formula O2 represents oxygen gas — two atoms 



1.^4 PRACTICAL CHEMISTRY 

united into one molecule. Whereas O represents an un- 
comhined atom of oxygen ; the free atom is in a more active 
chemical state, called the nascent state, because an atom 
of oxygen just liberated from a compound is ready, so to 
speak, to oxidize. 

Another source of chlorine for bleaching is sodium hypo- 
chlorite (NaClO). This compound is prepared by passing 
a current of electricity through sodium chloride solution 
and allowing the products to react, thus : — 



2NaOH 


+ ci, 


= NaClO + NaCl + HoO 


Sodium 


Chlorine 


Sodium Sodium Water 


Hydroxide 




Hypochlorite Chloride 



Sodium hypochlorite is unstable, and a cold dilute solution 
contains hypochlorous acid, owing to the interaction of the 
compound with water, thus : — 



NaClO + 


HoO 


HCIO + 


NaOH 


Sodium 


Water 


Hypochlorous 


Sodium 


Hypochlorite 




Acid 


Hydroxid( 



The hypochlorous acid furnishes nascent oxygen. Sodium 
hypochlorite solution is used by up-to-date laundries. 

150. The process of bleaching. — Bleaching is an ox- 
idizing process. Oxygen, as we have just seen, is liberated 
in the nascent state from hypochlorous acid and readily 
decomposes the colored substances and changes them into 
colorless compounds. 

A conventional diagram of the process of bleaching cotton cloth 
is shown in Y\g. 64. The pieces arc sewed together end to end in 
long strips and drawn by machinery from the roll .1 successively 
through vats containing bleaching powder solution B, weak acid C, 
and water D. At some point toward the end of the process the cloth 
passes through a vat containing acid sodium sulphite solution (or 



CHLORINE — HYDROGEN CHLORIDE 



135 



similar mixture) E, called the antichlor, to remove traces of hypo- 
chlorous acid. After thorough washing, the cloth is dried and ironed 
by passing over hot cylinders FG , and finally wound on the roll H. 

The chemical process of bleaching can be shown in the laboratory 
by a simple experiment. Put a little bleaching powder in the beaker 




Fig. 64. — Diagram of the process of bleaching cotton cloth 

A (Fig. 65), fill the beaker about one third full of water, and mix 
well. Fill the beaker B one third full of dilute sulphuric acid ; and 
the beaker C one third full of water. Press the lower half of the 
strip of colored cloth into the bleaching powder solution and then into 
the acid, passing it back and forth several times. Finally wash the 
cloth thoroughly in the water in C. The bleached cloth should have 
the general appearance shown in Fig. 65. 

151. Uses of chlorine. — 

Besides the use of chlorine 
in the manufacture of bleach- 
ing powder and 



bleaching 





Fig. 65. — Bleaching colored 
cloth 



Fig. 66. — Fire ex- 
tinguisher con- 
taining carbon 
tetrachloride 



mixtures, large 
Ciuantities of 
the gas are 
made into use- 
ful compounds 
of chlorine. One is carbon tetrachloride 
(CCI4), which is used in ''pyrene" fire ex- 
tinguishers (Fig. 66), and also as a solvent 
for extracting greases ; the non-inflammable 
cleaning mixture called '' carbona " con- 
tains carbon tetrachloride. Chlorine is 
also used in making disinfectants and 



m 



purifying water (69 and Fig. 35). 



136 



PRACTICAL CHEMISTRY 



152. Hydrogen chloride and hydrochloric acid. — 
Hydrogen chloride is a gas, which is very soluble in water. 
Hydrochloric acid is the common name of a water solution 
of hydrogen chloride. This solution is known commer- 
cially as muriatic acid (from the Latin word muria, meaning 
brine), but it is more properly called hydrochloric acid. 
Hydrogen chloride is often called hydrochloric acid gas. 

153. Preparation of hydrogen chloride. — This gas is 
prepared from sodium chloride by heating with sulphuric 
acid. If the mixture is gently heated, the chemical change 
is represented thus : — 



NaCl 

Sodium 
Chloride 



+ 



H2SO4 = 

Sulphuric 
Acid 



HCl 

Hydrogen 
Chloride 



+ 



HXaS04 

Acid Sodium 
Sulphate 



But at a high temperature the equation is 
2NaCl + H2SO4 = 2HCI 



+ Na2S04 

Sodium Sulphate 

The solution is prepared by passing the gas into water. 

154. Hydrochloric acid is manufactured in enormous 
quantities by a method essentially like that used in the 
laboratory. 

The mixture of salt and sulphuric acid is put into the cast iron 
retort .4 (Fig. 67) and heated by the furnace 5 to a moderate temper- 
ature ; as soon as the 
>^' mass becomes pasty it 

is raked out upon the 
flat heater A' and 
heated to a high tem- 
perature by the fur- 
nace B'. The hydro- 
gen chloride escapes 




k 



Fig. 67. — Sketch of the apparatus for the through C and C into 
manufacture of hydrochloric acid an absorbing tower 



CHLORINE — HYDROGEN CHLORIDE 137 

filled with resistant material over which water trickles ; as the gas 
passes up the tower, it is absorbed by the descending water, and the 
solution flows out at the bottom as concentrated acid. 

Hydrochloric acid is also a by-product in the manufacture of 
sodium carbonate by the Leblanc {process (450). 

155. Properties of hydrogen chloride. - Hydrogen chlo- 
ride is a colorless gas. It has a choking, sharp taste, and 
irritates the Hning of the nose and throat. It is about 
1.25 times as heavy as air. A hter at 0° C. and 760 mm. 
weighs 1.64 gm. The gas becomes a colorless liquid when 
subjected to pressure and a moderately low temperature. 
The marked solubility of hydrogen chloride in water is 
one of its most striking properties. Even when it escapes 
into moist air, it forms white fumes which are really minute 
drops of a solution of the gas in the moisture of the air (147). 
At ordinary temperatures about 500 1. of gas dissolve in 
I 1. of water. 

The solubility of hydrogen chloride in water can be shown by a 
simple experiment. The apparatus is arranged as in Fig. 68. The 
flask A is filled with hydrogen chloride. The medicine dropper B is 
partly filled with water, the stopper with its tubes is inserted, and 
the flask is then arranged as shown in the figure. By pinching the 
bulb of the dropper, a few drops of water are forced into the flask. 
This small quantity of water dissolves so much gas that a partial 
vacuum is formed in the flask ; pressure within the flask is reduced 
so much that the atmospheric pressure forces water from the jar C up 
the tube D and through the small opening into the flask. 

156. Chemical conduct of hydrogen chloride. — Hy- 
drogen chloride does not burn nor support combustion. 
It is a very stable compound and can be heated to about 
1800° C. before it begins to decompose. Perfectly dry 
hydrogen chloride has httle or no chemical activity. 
Whereas the moist gas unites readily with certain sub- 
stances, e.g. ammonia gas ; in this case dense white clouds of 



138 



PRACTICAL CHEMISTRY 



0=<s 



ammonium chloride (NH4CI) arc formed. This reaction is 
sometimes used as a test for hydrogen chloride (173). 



157. Composition of hydrogen chloride. — 
Experiments show that hydrogen chloride is 
composed of hydrogen and chlorine in the 
ratio of I to I by volume. When a mixture of 
equal volumes of hydrogen and chlorine is ex- 
posed to the direct sunlight or to the action 
of an electric spark, the gases combine, hy- 
drogen chloride is formed with no residue, 
and the volume of the resulting gas equals the 
sum of the volumes of hydrogen and chlo- 
rine used. We express the volumetric rela- 
tions of hydrogen, chlorine, and hydrogen 
chloride by sa>mg: i volume of hydro- 
gen + I volume of chlorine = 2 volumes 
of hydrogen chloride. In the form of an 
equation, this fact becomes : — 




Fig. 68. — Hydrogen 
chloride fountain 



H2 + Clo = 2HCI 

I vol. of I vol. 2 vols, of 

Hydrogen Chlorine Hydrogen Chloride 



The simple volumetric relation of these three gases is a good illustra- 
tion of Gay-Lussac's law (93, 176). 

158. Hydrochloric acid. — The water solution of hy- 
drogen chloride is the common substance hydrochloric 
acid. The ordinary kind contains from 30 to 40 per cent 
(by weight) of hydrogen chloride, and is called concen- 
trated hydrochloric acid. Its specific gravity is about 1.2. 
In the laboratory we also use dilute hydrochloric acid, 
which is prepared from the concentrated acid by adding 
4 to 5 times its volume of water. 

Hydrochloric acid, like most members of the important 
class of compounds called acids, has a sour taste and reddens 



CHLORINE — HYDROGEN CHLORIDE 139 

blue litmus. It reacts with many metals, liberating hy- 
drogen and forming chlorides of the metals, thus : — 
Zn + 2HCI - Ho + ZnCl2 

Zinc Hydrochloric Hydrogen Zinc 

Acid Chloride 

It also forms chlorides by interaction with oxides and 
hydroxides of metals, thus : — 

CaO + 2HCI 
Calcium 
Oxide 



= CaClo + 


H,0 


Calcium 


Water 


Chloride 




= NaCl + 


H2O 


Sodium Chloride 


Water 



CaCOa = 


-- CaCh 


+ CO2 + H2O 


Calcium 


Calcium 


Carbon Water 


Carbonate 


Chloride 


Dioxide 



NaOH + HCl 

Sodium Hydroxide 

It interacts readily with carbonates. The equation in the 
case of calcium carbonate is : — 

2HCI + 

Hydrochloric 
Acid 

Hydrochloric acid is an indispen- 
sable compound, and is used in many 
industrial processes. Like other acids, 
it is sold in bottles holding 2.5 hters 
and in securely packed glass car- 
boys containing 10 or more gallons 
(Fig. 69). 

159. Aqua regia. - Hydrochloric ^g. ,^. _ ^ c^arboy 
acid and nitric acid interact and lib- of hydrochloric acid 
erate chlorine, thus : — packed for shipment 



MURIATIC ^ 

f;ii) J 






3HC1 + 


HNO3 


= 2CI + NOCl 


+ 


2H2O 


Hydrochloric 


Nitric 


Nascent Nitrosyl 




Water 


Acid 


Acid 


Chlorine Chloride 







A mixture of one volume of concentrated nitric acid and 
three volumes of concentrated hydrochloric acid is usually 



I40 PRACTICAL CHEMISTRY 

used. If such a mixture is added to a metal, the nascent 
chlorine (2 CD forms a chloride of the metal. (Compare 
with nascent oxygen, end of 149.) The alchemists named 
the mixtures aqua regia, meaning " royal water," to em- 
phasize the fact that it dissolves the '' noble " metal 
gold. Another name is nitro-hydrochloric acid. 

160. Chlorides are compounds of chlorine with other 
elements. They are formed, as we have already seen, by 
the direct combination of chlorine and metals (147) and by 
the interaction of hydrochloric acid with metaUic oxides 
or hydroxides (158). Most chlorides are soluble in water. 
But the chlorides of lead (PbClo), silver (AgCl), and one of 
the chlorides of mercury (HgCl) are not soluble; they 
are formed as insoluble solids, when hydrochloric acid 
or a soluble chloride is added to a solution of a lead com- 
pound, silver compound, or the proper mercury compound. 
Thus : — 

Pb(N03)2 + 2HCI = PbCL -i- 2HNO3 

Lead Nitrate Hydrochloric xVcid Lead Chloride Nitric Acid 

The formation of insoluble solids by double decompo- 
sition (and certain other changes) is called precipitation, 
and the soUd itself is called a precipitate. Precipitates 
often have properties which are readily determined. Thus, 
silver chloride is white and curdy, and soon turns purple 
in the light ; moreover it dissolves in ammonium hydrox- 
ide owdng to the formation of a complex soluble compound, 
which, however, is transformed by dilute nitric acid into 
silver chloride. Other chlorides have difTerent properties. 
Hence, the precipitation of silver chloride serves as a test 
for hydrochloric acid and soluble chlorides. 

A molecule of a chloride may contain one or more atoms of chlorine 
and occasionally the name of the compound indicates this fact, e.g. 



CHLORINE— HYDROGEN CHLORIDE 141 

manganese dichloride (MnCl-j), antimony trichloride (SbCls), carbon 
tetrachloride (CCU). If the same metal forms two chlorides, the 
two are distinguished by modifying the name of the metal ; the one 
containing the smaller proportion of chlorine ends in -ous, that con- 
taining the larger in -ic. Thus, mcrcurous chloride is HgCl, and 
mercuric chloride is HgClo. 

EXERCISES 

1. Prepare a summary of (a) chlorine and (b) hydrochloric acid. 

2. Sketch from memory the apparatus used to prepare chlorine 

(a) on a large scale, and (b) in the laboratory. 

3. How can chlorine be quickly distinguished from the gases pre- 
viously studied ? 

4. Summarize the chemical conduct of chlorine. 

6. Topics for home study, (a) Nascent state, (b) Chlorine 
water, (c) Liquid chlorine, (d) Chlorine is an oxidizing agent. 

6. What is (a) muriatic acid, (b) chloride of lime, (c) bleaching 
powder? 

7. State the equation for (a) preparation of chlorine, (b) interaction 
of chlorine and water, {c) decomposition of hypochlorous acid, (d) prep- 
aration of hydrogen chloride, (e) interaction of hydrogen chloride and 
ammonia, (/) interaction of sodium chloride and silver nitrate. 

8. Write an essay on " bleaching with chlorine." 

9. Complete and balance these equations : (a) XaCl + H2SO4 

= + Xa2S04 ; (b) H2 + = HCl ; (c) HCl + Xa.COs = 

+ CC2 + ; (d) HgXOs H = HgCl + HXO3. 

PROBLEMS 

1. Calculate the weight of chlorine in (a) 2 kg. of sodium chloride. 

(b) 2 mg. of calcium chloride, (f) i gm. of aluminium chloride. 

2. How many grams of each product are formed when hydrochloric 
acid interacts with 85 gm. of manganese dioxide? 

3. (a) What is the weight of 15 1. of chlorine gas measured at 20° C. 
and 790 mm. ? (b) How many grams of potassium chloride are needed 
to prepare the weight of chlorine found in (a) ? 

4. How many grams of hydrogen chloride can be obtained from 
27 gm. cf sodium chloride? How many liters (standard conditions)? 

5. Calculate the percentage composition of (a) KCl, (b) CaCU. ' 

6. How much sodium chloride can be formed by burning sodium 
in 40 gm. of chlorine? 

7. Calculate the simplest formula from (a) Hg = 84.92, CI = 15.07; 
(6) Hg = 73.8, CI = ^6.2. 



CHAPTER XII 
ACroS, SALTS, AND BASES 

161. What are acids ? — Hydrochloric acid is an ex- 
ample of an important class of compounds called acids. 
The general properties of hydrochloric acid are charac- 
teristic of the class. 

Hydrogen is a constituent of all acids — an essential 
constituent. The hydrogen of acids can be replaced by 
certain metals ; and the compound formed by this replace- 
ment is called a salt. Many compounds have hydrogen 
as a constituent, but they are not classed as acids unless 
they form salts by replacement of the hydrogen by a metal. 
Thus, water and sugar contain hydrogen, but the hydrogen 
in water does not form a salt by replacement of its hy- 
drogen by a metal, nor can the hydrogen in sugar be re- 
placed by a metal. Furthermore, most acids have a sour 
taste and change the color of a dye called htmus from 
blue to red. Substances which act thus on blue htmus 
are said to have an acid reaction. 

The presence of acids is often conveniently detected by the litmus 
test. For example, vinegar, pickles, many fruits, and some wines 
have a sour taste and turn blue litmus red. 

Other common acids are sulphuric (H2SO4), nitric 
(HNO3), and acetic (HC2H3O2). 

162. What are salts? — These compounds are not sour, 
nor do they, as a rule, have any effect on either blue or 
red htmus. Substances which have no effect on litmus 

142 



ACIDS, SALTS, AND BASES 143 

are often described as havin"; a neutral reaction. Many- 
salts have the taste associated with a famiUar member 
of this class, viz. common salt or sodium chloride ; a few 
are sour and some are bitter. This class of compounds 
has many members and their properties are somewhat 
varied. 

Salts invariably have a metal and a non-metal as con- 
stituents, and most salts also have oxygen. Chlorides are 
examples of salts which have only a metal and the non- 
metal chlorine as constituents, e.g. zinc chloride (ZnClo), 
sodium chloride (XaCl), calcium chloride (CaCb). Ex- 
amples of salts composed of a metal, a non-metal, and also 
oxygen are potassium chlorate (KCIO3) and sodium sul- 
phate (NaoS04) ; these compounds are salts of chloric acid 
and sulphuric acid respectively. 

163. What are bases? — Hydroxides are examples of the 
class of compounds called bases. Thus, sodium hy- 
droxide (NaOH) IS a typical base. Solutions of bases turn 
red Ktmus blue — just the opposite of acids, and are said to 
have a basic or an alkaline reaction. Solutions of strong 
bases {e.g. sodium hydroxide and potassium hydroxide) 
have a slippery feeUng and a biting, caustic taste. 

Bases are composed of a metal, oxygen, and hydrogen, 
e.g. sodium hydroxide (NaOH). The oxygen and hy- 
drogen are the essential part of a base, just as hydrogen is 
of an acid. In fact, the oxygen and hydrogen of a base 
act as a unit in many chemical changes. This group of 
atoms (OH) is called hydroxyl. And since hydroxy 1 is 
the root or foundation of a class of compounds, it is called 
a radical. 

164. Neutralization. — Acids, salts, and bases have 
fundamental chemical relations. When we mix solutions 
containing weights of an acid and a base proportional to 



144 PRACTICAL CHEMISTRY 

their molecular weights, the acid and base interact com- 
pletely. The final solution has none of the characteristic 
properties of an acid or a base, but it does have the prop- 
erties of a salt. That is, the acid and base destroy the 
marked properties of each other, and a salt is produced. 
The acid and base neutrahze each other. For example, 
when . hydrochloric acid and sodium hydroxide interact, 
sodium chloride and water are formed. The equation for 
the reaction may be written : — 

Acid Base Salt Water 

HCl + NaOH = NaCl + HoO 

Hydrochloric Sodium Sodium Water 

Acid Hydroxide Chloride 

A chemical change in which an acid and a base neutralize 
each other and form a salt and water is called neutrali- 
zation. 

Neutralization illustrates double decomposition. In the 
chemical change just cited both the hydrochloric acid and 
the sodium hydroxide are decomposed and their parts are 
recombined in a different way, i.e. sodium chloride and 
water are the new compounds resulting from the recom- 
bination. 

Neutralization is usually done by means of burettes. These are 
graduated glass tubes, so marked that any desired portion of the 
contents can be drawn off by the stop-cock at the lower end (Fig. 70). 
In using burettes for neutralization, one is filled to the zero (upper) 
mark with a solution of an acid and the other with a solution of a 
base — one solution being of known concentration. A measured 
portion, say 15 cubic centimeters of the base, is drawn off into a 
beaker, several drops of litmus solution are added, and the acid is 
slowly dropped in with constant stirring until one drop more 
shows by the change in color (after thorough stirring) that the right 



ACIDS, SALTS, AND BASES 



145 



proportions of acid and base are present, i.e. that neutralization has 
occurred. If this solution is evaporated, nothing but a salt will be 
found in the residue. 

If we wish to find the strength of the acid, the volume of acid is 
read accurately. Knowing the concentration (and volume) of the 
base solution and the volume of the acid solu- 
tion, we can calculate the exact weight of the 
acid needed for the neutralization of the base, 
and from this weight we can find the strength of 
the acid solution. 



QP=^=^ 




Fig. 70. — Burettes 



165. Another definition of a salt. — 

For the present, we may regard salts as 
compounds formicd from acids and bases 
by neutralization. That is, the metal 
of the base unites with the non-metal 
or non-metallic group of the acid, e.g. 
Na of NaOH unites with NO3 of HNO3 
to form the salt NaNOs. The nature 
and interrelation of acids, salts, and 
bases will be further discussed. (See Chapter XVIII.) 

166. Naming acids, salts, and bases. — There are three 
other non-oxygen acids besides hydrochloric acid, viz. hy- 
drofluoric (HF), hydrobromic (HBr), and hydriodic (HI). 
The salts corresponding to these four acids end in ide. e.g. 
chloride, fluoride, bromide, and iodide. Sometimes the 
compound commonly known as hydrogen sulphide (H2S) 
is called an acid, and its salts are called sulphides. 

Oxygen is a constituent of most acids and salts, and the 
names of the oxy-acids and oxy-salts are related, especially 
the suffixes. This relation can be best illustrated by the 
chlorine acids that contain oxygen. These acids are 
hypochlorous (HCIO), chlorous (HCIO2), chloric (HCIO3), 
and perchloric (HCIO4). In forming the names of the 
corresponding salts the suffix ous becomes ite, while ic be- 



146 PRACTICAL CHEMISTRY 

comes ate; the prefixes are not changed. Thus, the names 
of the corresponding sodium salts are sodium hypochlorite, 
chlorite, chlorate, and perchlorate respectively. In the 
case of the acids of some elements the body of the name 
is modified, e.g. sulphuric becomes sulphate (not sulphur- 
ate!), and phosphoric becomes phosphate (not phosphor- 
ate!).. Hence we may say briefly, ous becomes ite and ic 
becomes ate in changing names of acids to the corresponding 
salts. 

Bases are distinguished by placing the name of the metal 
before the word hydroxide, e.g. sodium hydroxide (NaOH), 
calcium hydroxide (Ca(0H)2). 

167. Conclusion. — More will be learned about acids, 
bases, and salts, especially in Chapter XVIII and under 
typical examples of these compounds. 

EXERCISES 

1. Prepare a summary of this chapter. 

2. State some characteristics of (a) acids, (b) bases, (c) salts. 

3. How are acids, bases, and salts related? 

4. Give the name and formula of three common (c) acids, and 

(b) bases, (c) Of five salts. 

5. Define and illustrate neutralization. 

6. What is hydroxyl? 

7. Give the name and formula of the sodium salt of hydrochloric 
acid. Also of the corresponding salt of potassium, aluminium, lead, 
silver, antimony, manganese, zinc, and barium. 

8. Apply Exercise 7 to (a) nitric acid, (b) nitrous acid, (c) hypo- 
chlorous acid. 

9. Apply Exercise 7 to (a) sulphuric acid, (b) sulphurous acid, 

(c) permanganic acid. 

10. Give the name and formula of the hydroxide of the metals enu- 
merated in Exercise 7. 

11. Give the name of these : (a) potassium salt of chloric acid 
(b) calcium salt of hypophosphorous acid, (c) sodium salt of carbonic 
acid, (d) lead salt of chromic acid, (c) zinc salt of hydriodic acid, (/) po- 
tassium salt of perchloric acid, (g) iron salt of hydrochloric acid, (h) so- 
dium salt of hydrofluoric acid, (i) calcium salt of persulphuric acid, 



ACIDS, SALTS, AND BASES 147 

{j) potassium salt of hydrobromic acid, (k) calcium salt of hydrofluoric 
acid, (/) sodium s^lt of hypophosphorous acid. 

12. Classify into acids, bases, and salts: KOH, HBr, NH4OH, 
NaXOs, H3P64, Ag2S04, Ca{OH).,, HI, Pb(0H)2, FeCls, Zn(X03)2, 
Cu(0H)2, KCIO4, NazCOa, BaS04, BaCl^, A1(0H)3. 

PROBLEMS 

1. Calculate the per cent of hydrogen in {a) hydrochloric acid, 
(ft) sulphuric acid, (t) nitric acid. 

2. Calculate the per cent of hydroxyl in (a) sodium hydroxide, 
(h) potassium hydroxide, (c) ammonium hydroxide, (d) calcium hydrox- 
ide. 

3. How many grams of . hydroxyl correspond to (a) 35 gm. of 
A1(0H)3, (b) 80 gm. of barium hydroxide? 

4. What weight of nitric acid is needed to neutralize 27 gm. of 
the base corresponding to {a) Ca, (b) sodium, (c) K? 

5. Two solutions are well mixed. One contained 75 gm. of sul- 
phuric acid, and the other 75 gm. of sodium hydroxide. What will be the 
weight of the compounds (other than water) in the final solution? 

6. Complete and balance : (a) BaO -\ = Ba(0H)2; (b) XH4I 

+ = Agl + (NH4)2S04; (c) Pb(N03)2 + = PbCl2 + . 

7. Calculate the formula corresponding to: (a) Ca = 29.41, 
S = 23.52, O = 4705; (b) Xa = 39.31, CI = 60.68. 

8. What weight of the salt is formed in these cases of neutraliza- 
tion? (a) Hydrochloric acid and 10 gm. of potassium hydroxide; 
(b) sulphuric acid and 37 gm. of sodium hydroxide. 

9. Suppose 37.5 cc. of a hydrochloric acid solution neutralize 30 cc. 
of a sodium hydroxide solution, and that each cc. of the sodium hydrox- 
ide solution contains 0.003 S^- of the base. What weight of hydro- 
chloric acid is contained in the acid solution? 



CHAPTER XIII 

AMMONIA — AMMONIUM HYDROXIDE — AMMONIUM 
COMPOUNDS 

168. Introduction. — The term ammonia includes both 
the gas (XH3) and its sokition in water (NH4OH). Some- 
times the solution is called ammonia water, though its 
scientific name is ammonium hydroxide. Ammonium 
hydroxide is an example of a base (163). 

169. Formation of ammonia. — When vegetable and 
animal matter containing nitrogen decays, the nitrogen 
and hydrogen are usually Hberated as the compound am- 
monia. The odor of ammonia can be detected near stables. 
If animal substances containing nitrogen are heated (es- 
pecially with lime or soda-lime), ammonia is given oE. 
(The formation of ammonia in this w^ay is a test for com- 
bined nitrogen. See 114.) Soft coal contains combined 
nitrogen and hydrogen, and' when the coal is heated, as 
in making illuminating gas, ammonia is liberated. This 
is one source of commercial ammonium hydroxide. 

170. Preparation of ammonia gas in the laboratory. — 
Ammonia gas is prepared in the laboratory by heating 
ammonium chloride w^ith a base, usually moist calcium 
hydroxide. The equation for the reaction is: — 

2NH4CI + Ca(0H)2 = 2NH4OH + CaClo 

Ammonium Calcium Ammonium Calcium 

Chloride Hydroxide Hydroxide Chloride 

The ammonium hydroxide is unstable, especially when 

148 



AMMONIA — AMMONIUM COMPOUNDS 149 



heated, and quickly decomposes into ammonia and water, 
thus : — 

NH4OH = XH3 + H.O 



Ammonium Hydroxide Ammonia 



Water 



The gas is very volatile, and is usually collected by upward 
displacement, i.e. by allowing the gas to flow upward into 
a bottle and displace the 
air (Fig. 71). The solution 
is prepared by conducting 
the gas into water. 

171. Manufacture of 
commercial ammonium 
hydroxide. — The am- 
monia gas from which 
commercial ammonium 
hydroxide is manufactured 
is obtained mainly from 
the illuminating gas works. 
When coal is heated in 
closed retorts, a mixture of 
gases is liberated contain- 
ing ammonia. The am- 
monia is separated from the other gases by dissolving 
it out with water (326). This impure solution, which 
is called ammoniacal liquor or gas liquor, is treated with 
lime to liberate the ammonia, which is absorbed in tanks 
containing hydrochloric acid or sulphuric acid. This so- 
lution upon the addition of a base (e.g. calcium hydroxide) 
gives up its ammonia, which is dissolved in distilled water, 
forming thereby the ammonium hydroxide of commerce. 

Some ammonia is obtained from the gases Hberated from 
coke ovens. Ammonia is also manufactured by the direct 
combination of nitrogen and hvdro^ren fl74. 175). 




Fig. 71. — Apparatus for preparing 
ammonia in the laboratory 



I50 PRACTICAL CHEMISTRY 

172. Properties of ammonia. — Ammonia gas is color- 
less. It has an exceedingly pungent odor, and if inhaled 
suddenly or in large quantities, it brings tears to the eyes 
and may cause suffocation. It is a light, volatile gas, 
being about one half (0.59) as heavy as air. A hter of the 
gas at 0° C. and 760 mm. weighs 0.77 gm. Ammonia gas 
is easily hquefied — 0° C. and 4.2 atmospheres {i.e. 4 X 760 
mm.) being the usual conditions. Liquefied ammonia 
is often called anhydrous ammonia, because it contains 
no water.. It boils at —34° C. Hence, if it is exposed 
to the air or warmed in any way, it changes into the gas, 
and in so doing absorbs considerable heat. This fact has 
led to the extensive use of Uquid ammonia in refrigera- 
tion and in the manufacture of ice (177). 

Ammonia gas is very soluble in water, even more so than 
hydrogen chloride ; and its solubihty can be shown by the 
" fountain " experiment. (See Fig. 68.) A hter of water 
at 0° C. dissolves 1148 1. of gas (measured at 0° C. and 
760 mm.), while at ordinary temperature i 1. of water dis- 
solves about 700 1. of gas. This solution of the gas is often 
called ammonia, though other names, e.g. ammonium hy- 
droxide and ammonia water are sometimes applied to it 
(168) ; it gives off the gas freely, when heated, as may 
be easily discovered by the odor or by the formation of 
dense white fumes of ammonium chloride (NH4CI) when 
the solution is exposed to hydrochloric acid (156). The 
commercial solution called ammonia is lighter than water 
(its specific gravity being about 0.88) and contains 
approximately 35 per cent (by weight) of the compound 
NH3. 

173. Chemical conduct of ammonia. — Ammonia gas 
will not burn in air under ordinary conditions, nor will it 
support combustion, as the term is usually used ; but if the 



AMMONIA — AMMONIUM COMPOUNDS 1 5 1 

air is heated or if its proportion of oxygen is increased, a 
jet of ammonia gas will burn in it with a yellowish flame. 
When electric sparks are passed through ammonia gas, 
it decomposes to some extent into nitrogen and hydrogen ; 
whereas nitrogen and hydrogen form a small amount of 
ammonia under the same conditions (174. 175). 

Ammonia reacts with certain elements. Dried ammonia 
gas and heated magnesium form magnesium nitride and 
hydrogen, thus : — 

2NH3 + 3Mg = MgsNo + 3H2 

Ammonia Magnesium Magnesium Nitride 
Ammonia and chlorine interact, thus : — 

2NH3 + 3CI.2 = No + 6HC1 

Ammonia Chlorine Nitrogen Hydrochloric Acid 

Ammonia combines directly with water, form^ing ammo- 
nium hydroxide, thus : — 

NH3 + H.2O = NH4OH 

Ammonia Water Ammonium Hydroxide 

It also combines with certain gases, e.g. hydrogen chloride 
(HCl) , thereby forming ammonium chloride (NH4CI) . This 
reaction serves as a test for ammonia gas. (Compare 156.) 
174. Synthesis of ammonia from its elements. — Ni- 
trogen and hydrogen unite if electric sparks are passed 
through a mixture of these gases. The equation is : — 
No + 3H2 = 2NH3 

The amount of ammonia formed in a given case, however, 
is only a small per cent of that indicated by the equation. 
The small yield is due partly to the fact that ammonia 
itself decomposes into nitrogen and hydrogen. Thus, we 
may write this equation : — 

2NH3 = No + 3H2 



152 PRACTICAL CHEMISTRY 

If we compare these equations, we see that one is the re- 
verse of the other. This means that one reaction undoes 
the work of the other. When the experiment is done in 
a closed tube, the two reactions proceed at the same time 
— one reversing the other. Such a complete reaction is 
called a reversible reaction. The equation for a reversible 
reaction contains oppositely pointed arrows in place of 
the equaHty sign. The equation for this reversible re- 
action is : — 

N2 + 3H2 :^ 2NH3 

This equation is read : nitrogen and hydrogen react re- 
versibly to form ammonia. 

A reversible reaction under a given set of conditions 
proceeds to equilibrium. This means that the amounts 
of the substances involved in both reactions increase or 
decrease until the quantity of any one substance formed 
equals the quantity of it which is transformed. In the 
case of ammonia, the mixture at equilibrium is only about 
2 per cent ammonia (and 98 per cent nitrogen and hydro- 
gen). If the ammonia is removed by adding acid or water 
to the apparatus, or by some other device, its removal dis- 
places the equilibrium and the reaction proceeds to com- 
pletion, i.e. all, or practically all, the nitrogen and hydrogen 
combine. (See also 196.) 

175. Manufacture of ammonia from nitrogen and hy- 
drogen. — The reaction described in 174 for the manufacture 
of ammonia proceeds too slowly. To be profitable com- 
mercially, the reaction must be hastened, that is, its veloc- 
ity must be increased so that more ammonia will be formed 
in a given time. Several factors affect the velocity of a 
reaction, e.g. temperature, pressure, and experimental con- 
ditions. In manufacturing ammonia, the best conditions 



AMMONIA — AMMONIUM COMPOUNDS 153 



are a temperature of about 450° C. and a pressure of about 
200 atmospheres (i.e. 200 X 760 mm.). This reaction, as 
well as many others, is further hastened by passing the 
heated and compressed gases over a catalyst (53) — in 
this case essentially finely divided iron. 

The mixture of ammonia, nitrogen, and hydrogen is 
passed, still under pressure, through water, which dissolves 
the ammonia, while the other gases 
are returned to the apparatus. The 
ammonia solution is drawn off when it 
becomes saturated (under ordinary pres- 
sure and temperature). Ammonia made 
directly from its elements is called syn- 
thetic ammonia. 

176. Composition of ammonia. — Experi- 
ments show that ammonia is a compound of 
nitrogen and hydrogen, especially its synthesis 
from these elements. By utilizing the fact 
that ammonia and chlorine react and Hberate 
nitrogen, the volumetric composition of am- 
monia can be shown to be nitrogen is to hydro- 
gen as I to 3. A supplementary experiment Fig. 72. Appara 

shows that two volumes of ammonia arc formed tus for deter 
by the union of one volume of nitrogen and 
three volumes of hydrogen. 

The volumetric composition of ammonia may 
be expressed thus : — 

N2 -f- 3H2 = 2NH3 

I vol. of 3 vols, of 2 vols, of 

Nitrogen Hydrogen Ammonia 



mining the volu- 
metric composi- 
tion of ammonia 
gas by the inter- 
action of ammo- 
nium hydro.xide 
and chlorine 



The simple volumetric relation of these three gases is a good example 
of Gay-Lussac's law (93, 157). 

In demonstrating the volumetric composition of ammonia, a tube 
of known volume (Fig. 72) filled with chlorine is provided with a 
funnel through which concentrated ammonium hydroxide is slowly 
dropped into the chlorine, until the reaction ceases. After the ex- 



154 



PRACTICAL CHEMISTRY 



cess of ammonium hydroxide is neutralized with sulphuric acid, the 
volume of nitrogen left is found to be one third of the original volume 
of chlorine. Now hydrogen and chlorine combine in equal volumes 
(157). Hence the volume of hydrogen withdrawn from the ammonia 
must be equal to the original volume of chlorine. But this volume is 
three times the volume of the nitrogen, therefore there must be three 
times as much hydrogen as nitrogen in ammonia gas. 

177. Ammonia as a refrigerant. — The use of ammonia 
in producing low temperatures depends upon the fact that 
liquefied ammonia (not ordinary ammonia solution) changes 
rapidly into a gas when its pressure is reduced, and in so do- 
ing absorbs heat from the surrounding air or liquid. Hence, 




Fig. 73. — Apparatus for using liquefied ammonia to produce low 
temperatures 

if liquefied ammonia is allowed to flow through a pipe im- 
mersed in a solution of sodium chloride or calcium chloride 
(technically called a brine), the ammonia evaporates in 
the pipe and cools the brine, which may be used directly 
as a refrigerant or for making ice. In some cold storage 
plants, packing houses, and sugar refineries, this cold brine 
is circulated through pipes placed in the storage rooms 
where a low temperature is desired. 

The construction and general operation of an ice-making plant is 
shown in Fig. 73. Liquefied ammonia is forced from a tank into a 
series of pipes which are submerged in a large vat A nearly filled with 



AMMONIA — AMMONIUM COMPOUNDS 155 

brine. Metal cans containing pure water to be frozen are immersed 
in the brine, which is kept below the freezing point of water by rapid 
evaporation of the ammonia in the pipes. After several hours the 
water in the cans is frozen into cakes of ice. As fast as the ammonia 
gas forms in the pipes, it is removed by exhaust pumps (£) into another 
set of pipes C, where it is condensed into liquefied ammonia and con- 
ducted through D into the other set of pipes ready for renewed use. 
In cold storage plants the cold brine is circulated through pipes 
in the various rooms {B). 

178. Ammonium hydroxide. — When ammonia gas is 
passed into water, the ammonia combines with the water 
to some extent and forms a solution of an unstable com- 
pound having the composition represented by the formula 
NH4OH. This compound is ammonium hydroxide. Am- 
monium hydroxide is a base (163). Like other members 
of this class of substances it turns litmus blue. Concen- 
trated solutions have a slippery feehng. It also neutral- 
izes acids, thus : — 

NH4OH -1- HCl = NH4CI + H2O 

Ammonium Hydrochloric Ammonium Water 

Hydroxide Acid Chloride 

Ammonium hydroxide is widely used as a cleansing agent 
(especially for the removal of grease), and as a restorative 
in cases of fainting or of inhaling irritating gases; large 
quantities are consumed in dyeing and calico printing, 
and in the manufacture of dyestuffs, sodium carbonate 
and bicarbonate, and ammonium compounds. 

179. Ammonium compounds contain a group of atoms 
which acts chemically like an atom of a metal, especially 
the metals sodium and potassium. This group is called 
ammonium, and its formula is NH4. Ammonium has 
never been isolated from its compounds. Ammonium, 
like hydroxyl (163), is called a radical, because it is the 



156 PRACTICAL CHEMISTRY 

root or foundation of a series of compounds and in chemical 
changes passes from one ammonium compound to another. 
Ammonium compounds decompose when heated with 
an alkaU, such as sodium hydroxide or moist Hme, i.e. 
calcium hydroxide (170) ; ammonia gas is the conspicuous 
product. This reaction is a test for ammonium com- 
pounds. 

180. Ammonium chloride. — There are many ammo- 
nium salts. Thus, ammonium chloride (NH4CI) is the salt 
formed by the neutralization of ammonium hydroxide (a 
base) by hydrochloric acid (see 164). It is manufactured 
by passing ammonia (obtained from the ammoniacal liquor 
in gas works) into hydrochloric acid. The crude product 
is often called " muriate of ammonia " to indicate its re- 
lation to muriatic acid (the commercial name of hydro- 
chloric acid). It is used in Leclanche batteries, as an in- 
gredient of soldering fluids and of fertilizers. 

The crude salt is purified by heating it gently in a large iron pot 
with a dome-shaped cover ; the ammonium chloride volatilizes easUy 
and then crystallizes in the pure state as a fibrous mass on the in- 
side of the cover, whereas the impurities remain behind in the vessel. 
This process of purification is called sublimation. The product is a 
sublimate. Sublimed ammonium chloride is known as sal ammoniac. 

181. Other ammonium salts. — Ammonium sulphate ((NH4)2S04) 
is made by passing ammonia gas into sulphuric acid, or by adding 
ammonium hydroxide to the acid, thus : — 

2NH4OH + H0SO4 = (NH4)2S04 + HoO 

Ammonium Hydroxide Ammonium Sulphate 

The commercial salt is a grayish or yellowish solid and is obtained in 
large quantities as a by-product of coal gas manufacture. It is used 
as an ingredient of fertilizers, since it is a cheap, soluble salt containing 
considerable nitrogen (116). Ammonium nitrate (NH4NO3) is made 
by passing ammonia into nitric acid, or by allowing ammonia gas and 
the vapor of nitric acid to mingle, thus : — 



AMMONIA — AMMONIUM COMPOUNDS 157 
NH3 + HXOx = NH4NO3 

Ammonia Nitric Acid Ammonium Nitrate 

When gently heated it decomposes into nitrous oxide (N2O) and water, 
and is used in the preparation of nitrous oxide. It is also used 
as an ingredient of certain explosives because it decomposes readily 
into volatile products. Ammonium carbonate ((NH4)2C03) is used 
in some kinds of baking powder, to scour wool, as a medicine, and in 
certain smelling salts (since it gives off ammonia readily). 

EXERCISES 

1. Prepare a summary of ammonia. 

2. How is ammonium hydroxide manufactured from (a) gas liquor, 
(b) nitrogen and hydrogen? 

3. State the conspicuous properties of ammonia gas. 

4. Describe the synthesis of ammonia. 

5. Define and illustrate (by ammonia) (a) reversible reaction 

(b) equilibrium, (c) displacement of equilibrium, (d) catalyst. 

6. State these reactions in the form of equations: (a) Prepar- 
ation of ammonium hydroxide from ammonium chloride and calcium hy- 
droxide, (b) Decomposition of ammonium hydroxide into ammonia 
and water, (c) Nitrogen and hydrogen react reversibly to form am- 
monia, (d) One volume of nitrogen and three volumes of hydrogen 
form two volumes of ammonia. 

7. What is (a) liquid ammonia, (b) anhydrous amrronia, (c) lique- 
fied amrfionia, {d) synthetic ammonia, (c) ammonia water? 

8. Describe the manufacture of ice by liquid ammonia. 

9. What is the volumetric composition of ammonia gas? How 
is it found? 

10. State the test for (a) ammonia, (b) ammonium compounds, 

(c) combined nitrogen. 

11. Topics for home study: (a) A cold storage plant, {b) Gay- 
Lussac's law. (c) Uses of ammonia, {d) Uses of ammonium com- 
pounds, (c) Equilibrium. 

PROBLEMS 

1. How many grams of ammonia (XH3) can be obtained from i kg. 
of ammonium chloride and sufficient calcium hydroxide? 

2. A pupil prepared five 250 cc. bottles of ammonia gas at 21° C. 
and 755 mm. What weight of materials interacted? 

3. What weight of ammonium chloride (95 per cent pure) is needed 
for the preparation of 60 gm. of NH3? Of 60 1. at 22° C. and 767 mm.? 



158 PRACTICAL CHEMISTRY 

4. What is the weight of 32 1. of ammonia gas at 20° C. and 
763 mm.? What volume will 32 gm. of ammonia gas occupy at the 
same temperature and pressure? 

5. To what weight and what volume of NH3 are 25 gm. of am- 
monium chloride equivalent (at standard conditions) ? 

6. What volume of ammonia gas will be liberated by the action of 
any base on 75 gm. of ammonium sulphate (at standard conditions)? 

7. How many liters of ammonia are formed by the complete inter- 
action of 9 1. of hydrogen and sufficient nitrogen? 

8. How many grams of ammonium chloride can be made from am- 
monium hydroxide and 100 gm. of the necessary acid? 

9. What formula corresponds to N = 26.17, H = 7.48, CI = 
66.35? 

10. Complete and balance : (a) NH4OH H = (XH4)2S04 

+ ; (b) NH3 + = N2 + HCl. 



CHAPTER XIV 



NITRIC ACm — NITRATES — NITROGEN OXIDES 



C=^3 



182. How nitric acid is formed. — Nitric acid (HNO3) 
is formed in small quantities when electric sparks are passed 
through air. Hence nitric acid or its salts can be detected 
in the atmosphere after 
a thunderstorm. This 
chemical change is ap- 
plied on a commercial 
scale in Norway (196). 
In another chemical pro- 
cess ammonia is oxidized 
(197). 

183. Preparation of 
nitric acid. — Nitric acid 
is prepared in the labora- 
tory by heating concen- Fig 
trated sulphuric acid 
with a nitrate, usually sodium nitrate (NaNOs). 

About equal weights of sodium nitrate and concentrated sulphuric 
acid are put into the glass retort (Fig. 74), and gently heated. The 
nitric acid is much more volatile than the sulphuric acid and distills 
into the receiver {e.g. a large test tube), which is kept cool by water, 
ice, or moist paper. 

The chemical change at a low temperature is expressed 
by the equation : — 

NaN03 + H.2SO4 = HNO3 + HNaS04 

Sodium Sulphuric Nitric .\cid Sodium 

Nitrate Acid Acid Sulphate 

159 




74. — .Apparatus for preparing 
nitric acid in the laboratory 



i6o 



PRACTICAL CHEMISTRY 



But if the temperature is high and an excess of sodium ni- 
trate is used, the equation is : — 

2NaN03 + H2SO4 = 2HNO3 + Na2S04 

At a high temperature part of the nitric acid decomposes ; 
hence excessive heat is usually avoided. 

184. Manufacture of nitric acid. — Nitric acid is man- 
ufactured by a process like that used in the laboratory. 
A sketch of the apparatus is shown in Fig. 75. 




Fig. 



Sketch of the apparatus for manufacturing nitric acid 



acid and sodium nitrate are heated in the cast iron retort, 
which is connected with glass or stoneware tubes in which 
the vapor is condensed by a current of cold water ; the 
tubes are arranged so that the nitric acid first condensed 
runs into a reservoir, while the vapors pass up a tower, 
where they are dissolved by descending water and flow- 
out at the bottom as dilute acid. (See 196, 197.) 

185. Properties of nitric acid. — Pure nitric acid is a 
colorless liquid, but the commercial acid is yellow or red- 
dish, due to dissolved nitrogen oxides. The acid that has 
been exposed to the sunlight is often yellow or brown, and 
if the light is intense, a brownish gas may often be seen in 
bottles of the acid. It is somewhat volatile, and the vapor 
dissolves readily in water ; hence the acid forms irritating 



NITRIC ACID — NITRATES t6i 

fumes when exposed to air, especially moist air. (See 
155.) 

Nitric acid mixes with water in all proportions. Com- 
mercial concentrated nitric acid contains about 68 per cent 
of the compound HXO.j, the rest being water. Such an 
acid has a specific gravity of 1.41 and boils at about 120° C. 

186. Chemical conduct of nitric acid. — Nitric acid is 
sour, turns blue litmus red, and forms salts — the nitrates. 
It is an unstable substance, and decomposes readily; 
among the decomposition products is a brown gas, nitrogen 
dioxide (NO2), which causes the yellow or brown color 
referred to above (185). If strongly heated, the decom- 
position is rapid ; the equation is : — 

4HNO3 = 4XO0 + O2 + HoO 

Nitric Acid Nitrogen Dioxide Oxygen Water 

Nitric acid is a very corrosive substance and reacts readily 
with many substances. With organic substances Hke 
hair, feathers, w^ooL silk, finger nails, and skin it forms a 
yellow compound. Hence nitric acid stains the skin, and 
often the clothing, yellow. The concentrated acid causes 
serious burns and should not be spilled on the hands or 
face. With other organic conipounds it forms explosives, 
such as nitroglycerin and nitrocellulose. 

One of the decomposition products of nitric acid is oxy- 
gen. Hence nitric acid is an oxidizing agent. Usually 
the oxygen is not liberated as a gas, but oxidizes whatever 
oxidizable substance is present. In order to emphasize 
the fact that oxidizing oxygen is available, the equation 
is written thus : — 

2HNO3 = 3O + 2NO + HoO 

Nitric Acid Nascent Oxygen Nitric Oxide Water 



i62 PRACTICAL CHEMISTRY 

Thus, charcoal burns briUiantly in the hot acid, while straw, 
sawdust, hair, and similar substances are charred and even 
inflamed by it; some organic compounds, w^hen heated 
with nitric acid, are completely decomposed into carbon 
dioxide and water. In the mixture of concentrated nitric 
and hydrochloric acids called aqua regia, nitric acid acts 
as an oxidizing agent (159). The nitric acid oxidizes the 
hydrochloric acid to water and leaves the chlorine in the 
nascent condition. (Compare end of 149.) The equation 
is usually written : — 



HN03 


+ 3HCI = 


2H2O + 2CI + XOCl 


Nitric 


Hydrochloric 


Water Nascent Nitrosyl 


Acid 


Acid 


Chlorine Chloride 



Finally, it interacts readily and often violently with metals, 
metalHc oxides, and hydroxides. (Compare 158.) The 
products of these reactions vary, the essential ones being 
nitrates and nitrogen oxides (189). 

187. Uses of nitric acid. — Nitric acid is one of the com- 
mon laboratory acids. Large quantities are used in the 
manufacture of nitrates, dyestuffs, sulphuric acid, and 
explosives, and in etching copper plates. 

188. Nitrates. — Nitric acid forms salts called nitrates. 
They are prepared by the methods usually used for salts, 
i.e. the interaction of nitric acid and metals or metalhc 
oxides and the neutralization of hydroxides by nitric acid. 

Many nitrates "are white sohds ; those of copper, nickel, 
and cobalt are blue, green, and dark red respectively. The 
nitrates of most metals are soluble in water. Their solu- 
tions are frequently used in the laboratory. The solids 
behave in various ways when heated. Equations illus- 
trating typical reactions are : — 



NITRIC ACID — NITRATES 163 

2NaN03 = 2NaN02 + O2 ; 

Sodium Nitrate Sodium Nitrite 

2CU(X03)-: = 2CuO + 4NO2 + O2 
Copper Nitrate Copper Oxide Nitrogen Oxide 

Since many nitrates, when heated, give up oxygen, they 
are powerful oxidizing agents. Thus, when potassium 
nitrate is dropped on hot charcoal, the charcoal burns vigor- 
ously. This kind of chemical action is called deflagra- 
tion. 

Nitrates are also formed in the soil by the action of bac- 
teria on complex nitrogen compounds. This process, w^hich 
is called nitrification, is slow ; formerly this was the sole 
source of the potassium nitrate needed for gunpowder. 

189. The interaction of nitric acid and metals. — This 
action is exceedingly vigorous; for this reason, probably, 
the alchemists called the acid aqua fortis — strong water. 
The products of the reaction vary with the metal, the con- 
centration of the acid, and the temperature. Hydrogen 
as a rule is not liberated so that it can be collected, for it 
is oxidized at once to water by the nitric acid, whereas 
the nitric acid is reduced to nitrogen compounds. 

The interaction of nitric acid and copper will serve as 
an example of the common reactions. When moderately 
dilute nitric acid is poured on copper, a reddish brown gas 
is given off, and the nquid turns blue, owing to dissolved 
copper nitrate. The equation for the reaction is: — 

3CU -f 8HNO3 = 3Cu(N03)2 + 2NO + 4H2O 

Copper Nitric Copper Nitric Water 

Acid Nitrate Oxide 

This equation is made up of three equations, and the 



i64 PRACTICAL CHEMISTRY 

complete form conceals the way in which the reactions 
take place. The nitric acid first decomposes, thus : — 

(i) 2HNO3 = 30 + 2NO + HoO 

Nitric Acid Nascent Oxygen Nitric Oxide Water 

The nascent oxygen (149) next oxidizes the copper, thus : — 

(2) 3Cu + 30 = sCuO 

Copper Nascent Oxygen Copper Oxide 

The copper oxide then reacts with the nitric acid, thus : — 

(3) 3CUO + 6HNO3 = 3Cu(N03)2 + 3H2O 

Copper Oxide Nitric Acid Copper Nitrate Water 

Since 3O is formed in (i) and used in (2) and 3CUO like- 
wise in (2) and (3), these two terms should not appear in 
the complete equation ; the other terms make up the com- 
plete equation. 

Nitric oxide is represented as a product of the interaction 
of nitric acid and copper. If the reaction takes place in an 
open vessel, the nitric oxide, which is a colorless gas, com- 
bines with oxygen and forms the reddish brown nitrogen 
dioxide gas. The equation is : — 

2NO + Oo = 2NO2 

Nitric Oxide Oxygen Nitrogen Dioxide 

Hence we often speak of nitrogen dioxide as a product of 
the interaction of nitric acid and metals, though it is usu- 
ally a secondary product. 

190. The test for a nitrate (and of course for nitric acid) 
is not, as customary, made by producing a precipitate. 
It is a color test, and is made as follows : Add to the so- 
lution of the nitrate or the nitric acid in a test tube an equal 
volume of ferrous sulphate solution (freshly prepared from 
clean ferrous sulphate and cold water) ; mix well. In- 



NITRIC ACID — NITRATES 165 

dine the test tube, and pour concentrated sulphuric acid 
cautiously down the side of the test tube. A dark brown 
layer appears where the two liquids meet (Fig. 76), owing 
to the formation of a brown unstable com- 
pound which has the composition (approx- 
imately) 3FeS04.2NO. 

191. Nitrous acid (HNO2) is not easily obtained 
in the free state, owing to its instability, but its 
salts — the nitrites — are well known. Potassium _ 
nitrite (KNO2) and sodium nitrite (NaNOo) are ^. ^ ^ 
formed by removing part of the oxygen from the T ' '. . . , 
corresponding nitrate by heating alone (188) or ^^^ nitrates 
with lead. Nitrites give off yellow-brown fumes 

(NOo) readily when treated with sulphuric acid, and are thus easily 
distinguished from nitrates. 

192. Nitrogen oxides. — There are live nitrogen oxides. 
The three important ones are nitrous oxide (N2O), nitric 
oxide (NO), and nitrogen dioxide (NO2) ; there is also an 
oxide called nitrogen tetroxide (N2O4), which is a special 
form of nitrogen dioxide. 

193. Nitrous oxide (N2O) is prepared by heating am- 
monium nitrate. The equation for the reaction is : — 

NH4NO3 = N2O + 2H2O 

Ammonium Nitrate Nitrous O.xide Water 

This colorless gas has a faint but pleasant odor. It is sol- 
uble in water, and the solution has a sweet taste. It is 
easily liquefied by reducing the temperature and applying 
pressure, and is often used in this form to furnish the gas. 
The gas does not burn, but it supports the combustion 
of many well-burning substances, though not so vigor- 
ously as oxygen does. Thus, sulphur, unless well ignited, 
will not burn in nitrous oxide. In its power to support 



1 66 PRACTICAL CHEMISTRY 

combustion it resembles oxygen. It is distinguished from 
oxygen by its failure to form brown fumes (NO2) when 
mixed with nitric oxide (194). 

The most striking property of nitrous oxide is its efTect 
on the human system. If inhaled for a short time, it causes 
more or less nervous excitement, often manifested by 
laughter, and on this account the gas was called " laughing 
gas" by Davy, who first studied its properties in 1799. 
If breathed in large quantities, it produces temporary un- 
consciousness and insensibiUty to pain. The gas, mixed 
with a small proportion of air or oxygen, is often used as 
an anaesthetic in dentistry. 

194. Nitric oxide (NO) is usually prepared by the inter- 
action of copper and dilute nitric acid (sp. gr. 1.2). The 
complete equation (189) for the reaction is : — 

3CU + 8HNO3 = 2NO + 3Cu(N03)2 + 4H2O 

Copper Nitric Nitric Copper Water 

Acid Oxide Nitrate 

Nitric oxide is a colorless gas. It is a little heavier than 
air and only sHghtly soluble in water. Upon exposure to 
air, it combines at once with the oxygen, forming reddish 
brown fumes of nitrogen dioxide — a striking change. The 
equation for this reaction is : — 

2NO + 0-2 = 2NO2 

Nitric Oxide Oxygen Nitrogen Dioxide 

This property distinguishes nitric oxide from all other gases. 
It does not burn, nor support combustion, unless the burning 
substance (e.g. phosphorus or sodium) introduced is hot 
enough to decompose the gas into nitrogen and oxygen, 
and then, the liberated oxygen assists the combustion. 

195. Nitrogen dioxide (NO2) is the reddish brown gas 
formed by the direct combination of nitric oxide and oxy- 



NITRIC ACID — NITRATES 167 

gen (189 end). It is also produced by heating certain 

nitrates. 

Thus : — 

2Pb(N03)2 = 4NO2 + 2PbO + O2 
Lead Nitrate Nitrogen Dioxide Lead Oxide Oxygen 

The fumes of nitrogen cUoxide usually appear when ni- 
tric acid and metals interact, but, as stated in 194, the 
nitrogen dioxide is produced by a second reaction, viz. 
the combination of nitric oxide with the oxygen of the air. 
Nitrogen dioxide has a disagreeable odor, and it is poi- 
sonous if breathed in moderate quantities. It interacts 
with water and yields under ordinary conditions nitric 
oxide and nitric acid, thus : — 

3NO2 + H2O = 2HNO3 + NO 

Nitrogen Dioxide Water Nitric Acid Nitric Oxide 

(See 196.) It also dissolves in concentrated nitric acid, 
forming fuming nitric acid, which is an oxidizing agent. 

When the reddish brown gas is cooled, it gradually loses color and 
at about 26° C. becomes a yellow gas, which has the composition 
represented by the formula N2O4 and is called nitrogen tetroxide. 
Upon heating nitrogen tetroxide, the brown gas reappears, and at 
about 140° C. the gas is wholly nitrogen dioxide. Above 140° C. the 
brown color fades, owing to the decomposition of nitrogen dioxide 
into nitric oxide and oxygen. At ordinary temperatures the brown 
gas is a mixture of the two oxides. 

A simple demonstration of the relation between nitrogen diox- 
ide and tetroxide is readily made by collecting some nitrogen dioxide 
in a glass tube, closing the tube, and immersing the lower half in ice 
water. The gas in the lower part becomes yellow-brown (NO4) 
whereas in the upper part it remains reddish brown (NO2). 

196. Manufacture of nitric acid from nitrogen oxides. — 
If electric sparks are passed through air, nitrogen and oxy- 
gen unite, thus : — 



i68 



PRACTICAL CHEMISTRY 



(i) No + O2 = 2NO 

But the nitric oxide combines at once with oxygen, and 
forms nitrogen dioxide, thus : — 

(2) 2NO + O2 = 2NO2 

When nitrogen dioxide is added to water, nitric acid and 
nitric oxide are produced, thus : — 

(3) 3NO2 + H2O = 2HNO3 + NO 

These reactions are the basis of modern processes of making 
nitric acid from nitrogen oxides and water. 

Air is used in one process as a source of the nitrogen 
oxides. Two unusual conditions must be fulfilled in this 





L_A 




Fig. 77. — Sketch of the apparatus for the manufacture of nitric 
acid from nitrogen, oxygen, and water 

process. First, nitrogen and oxygen must be heated to 
a very high temperature (about 3000° C.) before they will 
unite to an appreciable extent. Second, the mixture of 
gases resulting from reaction (i) must be cooled very 
quickly. Reaction (i) is reversible, thus: — 

N2 + O2 :;=±: 2NO 
The maximum quantity (only about 5 per cent) of nitric 
oxide is obtained at about 3000° C. At this temperature 
equilibrium is reached, i.e. the relative proportions remain 
unchanged. (Compare 174.) But just as soon as the tern- 



NITRIC ACID — NITRATES 



169 



peraturc becomes lower, the reverse reaction (right to left) 
begins and the quantity of nitric oxide rapidly decreases. 
However, if the mixture is cooled very quickly, enough 
nitric oxide is left for the reaction with water. 







J 3R 



/til 

-Hi' 



Fig. 7 



spread out (left) and end view (right) 



A sketch of the apparatus is shown in Fig. 77 and certain parts are 
shown in detail in Fig. 78. Air is blown (by A) into the electric fur- 
nace B. Here it is raised to the proper temperature by passing 
through an electric arc. In order to provide a large heating surface, 
the arc is spread out by a magnet into a disk six feet in diameter (Fig. 
78, left). The electrodes usually are hollow and are kept cool by 
running water; graphite electrodes are also used. An end view 
(Fig. 78, ri^ht) shows the magnets and edge of the disk. The hot 
gases containing the nitric oxide from the furnace are suddenly cooled 
in C, pass through boiler D into the oxidizing chamber E, where nitro- 
gen dioxide is formed, and then into the tower F filled with tiles over 
which water trickles, where the nitric acid is produced. The dilute 
nitric acid is concentrated or converted (by limestone or lime) into 
calcium nitrate. The latter is used as a fertilizer, either alone or 
mixed with lime. 

197. Manufacture of nitric acid from ammonia. — 
In another process, ammonia is the starting point. A 
heated mixture of ammonia and air is passed into lire-brick- 
lined chambers containing a catalyst — usually platinum 
in the form of gauze. At about 600° C, the reaction, ex- 
pressed by the following equation, takes place : — 
4NH3 + 5O2 = 4NO + 6H2O 



I70 PRACTICAL CHEMISTRY 

The nitric oxide is cooled, mixed with air, and then, as in 
the other process, passed into towers through which water 
trickles, where the nitric acid is produced, thus : — 

4NO + 2H2O + 3O2 = 4HNO3 

EXERCISES 

1. How is nitric acid prepared in the laboratory? State the two 
equations. 

2. Describe the older process of manufacturing nitric acid. 

3. Summarize the properties of nitric acid. 

4. Explain: (a) nitric acid is an oxidizing agent ; (b) nitric acid 
is unstable. 

5. What is the test for (a) nitric acid, (b) a nitrate, (c) nitric oxide, 
(d) nitrous oxide, (e) nitrogen dioxide, (/) a nitrite? 

6. Describe the interaction of nitric acid and copper and state the 
equations. 

7. Summarize briefly the properties of nitrous oxide. 

8. Compare nitric oxide and nitrogen dioxide. 

9. How is nitrogen dioxide prepared? 

10. State the relation of nitrogen dioxide and nitrogen tetroxide. 

11. Describe fully the manufacture of nitric acid from (a) nitrogen 
oxides and (b) ammonia. 

12. Interpret the equation N2 + O2 ^^2_ 2NO. 

13. Complete and balance : {a) CuCOs H = Cu(N03)2 H 

+ ; (b) HNO3 + C = NO2 + + CO2. 

PROBLEMS 

1. Calculate the percentage composition of (a) nitric acid, {b) po- 
tassium nitrite, (c) sodium nitrate. 

2. Show how nitrous oxide, nitric oxide, and nitrogen dioxide illus- 
trate the law of multiple proportions. 

3. Calculate the formula and give the name of the compound cor- 
responding to (a) O = 76.19, H = 1.58, N = 22.22; (b) O = 47-52, 
K = 38.61, N = 13.86. 

4. If the specific gravity of a sample of nitric acid is 1.522, (a) what 
will 100 cc. weigh; (b) what volume must be taken to weigh 100 gm. ? 

5. How many liters of oxygen are needed to change 6 1. of nitric 
oxide to nitrogen dioxide? 

6. How much sodium nitrate is needed to form a ion of commercial 
nitric acid? (See end of 185.) 



CHAPTER XV 

MOLECULAR WEIGHTS AND FORMULAS 

198. Introduction. — Formulas and molecular weights 
have been used freely in the foregoing pages. In this 
chapter we shall consider the methods by which molecular 
weights and formulas are found by experiment. 

199. Gay-Lussac's law of gas volumes. — We have seen 
several times that the volumes of gases involved in a 
chemical change can be expressed by small whole num- 
bers (92, 93, 157, 176). These results may be summarized 
in a: — 

Table of the Combixatiox of Gases by Voli':^ie 



Volumes of Combining Gases 

2 volumes of hydrogerx 
I volume of oxygen 

I volume of chlorine 
I volume of hydrogen 

3 volumes of hydrogen 

1 volume of nitrogen 

2 volumes of nitrogen 
I volume of oxygen 

I volume of nitrogen 
I volume of oxygen 



Volumes of Gaseous Product 



volumes of water vapor 



•olumes of hydrogen chloride 



2 volumes of ammonia 



2 volumes of nitrous oxide 



2 volumes of nitric oxide 



It is clear from the above table that the volumes of the 
gases can be expressed by small whole numbers. This 



171 



172 PRACTICAL CHEMISTRY 

simple relation is true of all gas reactions, and, as we found 
in studying the volumetric composition of water (92, 93), 
it may be stated as Gay-Lussac's law, thus : — 

In a chemical change the volumes of the gases can he 
expressed by small whole numbers. 

This law applies only to gases. For example, carbon is not a gas, 
though it is frequently involved in reactions with gases, e.g. : — 

Carbon + Oxygen = Carbon Dioxide 
I vol. I vol. 

So we omit carbon as far as volume is concerned, and say carbon unites 
with I volume of oxygen (O2) to. form i volume of carbon dioxide 
(CO.2). 

200. Avogadro's theory. — In 181 1 the Italian physicist 
Avogadro proposed an explanation of the simple numerical 
relation of gas volumes. It is usually called Avogadro's 
theory and may be stated thus : — 

Equal volumes of gases under like conditions of temperature 
and pressure contain the same number of molecules. 

This theory means that a liter of oxygen contains just 
as many molecules as a liter of hydrogen, nitric oxide, or 
any other gas, if the temperature and pressure conditions 
are not altered. The actual number of molecules in the 
volume of the gas is not important, but the assumption 
that the number — whatever it may be — is the same in 
equal volumes is very important in chemistry. 

201. How Avogadro s theory is used in finding relative 
molecular weights. — By means of Avogadro's theory 
we can find the relative molecular weights of gases. Let 
us consider carbon dioxide and oxygen. A liter of carbon 
dioxide weighs 1.98 gm. and a liter of oxygen 1.43 gm. at 
0° C. and 760 mm. Therefore the weight of a liter of car- 
bon dioxide is (approximately) 1.38 times that of -^ liter of 
oxygen. Since a liter of each gas contains the same number 



MOLECULAR WEIGHTS AND FORMULAS 173 

of molecules, the weight of the carbon dioxide molecules 
is (approximately) 1.38 times the weight of the oxygen mole- 
cules. It is evident, then, that if we weigh equal volumes 
of gases (under like conditions of temperature and pres- 
sure), we obtain weights which are in the same relation 
as the weights of single molecules. 

202. How we find the approximate molecular weight 
of a gas. — In 201 we found that carbon dioxide molecules 
weigh (approximately) 1.38 times the weight of oxygen 
molecules. Obviously, we could calculate the (approximate) 
molecular weight of carbon dioxide if we knew the molec- 
ular weight of oxy^gen. The molecular weight of oxygen 
is 32. (See next paragraph.) We now calculate the 
(approximate) molecular weight of carbon dioxide by 
multiplying 32 by 1.38, i.e. 32 X 1.38= 44.16. Therefore 
44.16 is the (approximate) molecular weight of carbon 
dioxide. 

The molecular weight of oxygen is 32 for two reasons. 
First, a molecule of oxygen contains 2 atoms, as will be 
shown in 203. Second, an atom of oxygen weighs 16, be- 
cause this number has been adopted by chemists as the 
standard atomic weight (215). Hence the molecular weight 
of oxygen is 32 {i.e. 2 X 16). 

This method of finding molecular weights is called the 
vapor density method. The steps are (i) find the vapor 
density referred to oxygen, and (2) multiply this value 
by 32. The expression vapor density referred to oxygen means 
the number found by dividing the weight of a given 
volume of a gas or vapor by the weight of an equal volume 
of oxygen (measured at the same temperature and pressure). 
Thus, in the example given above the num])er 1.38 is the 
vapor density of carbon dioxide {i.e. i.q8 ^ 1.43^* 

One method of determining the approximate molecular 



T 74 PRACTICAL CHEMISTRY 

weight of a gas or a readily volatilized substance is now 
clear, viz. find the vapor density on the oxygen basis and 
multiply this value by 32, or 

Molecular Weight = Vapor Density referred to Oxygen X 32 

Molecular weights determined by this method are ap- 
proximate. That is, they do not exactly equal the sum 
of th€ weights of the atom^s in a molecule, i.e. the so-called 
theoretical molecular weight. The difference is due mainly 
to slight but unavoidable errors in the process. For ex- 
ample, the approximate molecular weight of carbon dioxide 
is 44.16, whereas the exact molecular weight is 44.00 (i.e. 
12 + (2 X 16)). The slight difference in this, and other 
cases, does not affect the validity and use of the weights 
found by this method. 

Some substances cannot be vaporized without decomposition. 
The molecular weights of such substances cannot, of course, be found 
by the vapor density method. If a substance dissolves without 
decomposition, its molecular weight can be determined by an appro- 
priate method (244). 

No experimental method, however, has been devised for deter- 
mining the molecular weight of a substance in the soHd state {i.e. not 
dissolved or vaporized) ; it is customary to assume that the molec- 
ular weight of such substances is the sum of the atomic weights 
in the simplest formula (109 and last paragraph in 206). 

203. How Gay-Lussac's law and Avogadro's theory 
are used to find the number of atoms in a molecule. — 
A molecule of oxygen contains two atoms. This conclusion 
is based mainly on the following argument : When oxy- 
gen and nitrogen combine to form nitric oxide, the 
volumes used and produced can be expressed thus : — 

Oxygen -f Nitrogen = Nitric Oxide 

I vol. I vol. 2 vols. 

Now according to Avogadro's theory, equal volumes of 



MOLECULAR WEIGHTS AND FORMULAS 175 

oxygen and of nitrogen contain the same num])er of mole- 
cules, while the two volumes of nitric oxide contain twice 
this number of molecules. We do not know the actual 
number of molecules in any of the volumes. Suppose, 
however, there are 1000 molecules of oxygen ; then by 
Avogadro's theory, there are 1000 molecules of nitrogen 
and 2000 molecules of nitric oxide, thus : — 

Oxygen + Nitrogen = Nitric Oxide 

1000 molecules 1000 molecules 2000 molecules 

Every molecule of nitric oxide must contain at least one 
atom of oxygen ; and the 2000 molecules must contain 
at least 2000 atoms of oxygen. But these 2000 atoms of 
oxygen were provided by the 1000 molecules of oxygen. 
Therefore, each molecule of oxygen must contain at least 
two atoms of oxygen. 

By a similar argument it can be shown that a molecule of nitrogen 
contains at least two atoms. So also it can be shown in the same way 
that a molecule of the common elementary gases contains at least 
two atoms. 

Furthermore, experiment shows that there is no reaction 
in which a given volume of the elementary gases, ox}^gen, 
nitrogen, hydrogen, and chlorine, provides material for 
more than two volumes of the gaseous product. This 
means there is no reaction in which a molecule of these 
gases is divided into more than two parts. And so we 
conclude that the molecule of these gases contains only 
two atoms. Hence we write their formulas Oo, N-j, Ho, 
and CI2. It is clear now why we used these formulas in 
preceding sections for molecules of the gases. 

204. What is a mole? — A mole of a substance is the 
number of grams numerically equal to its molecular weight. 
It is sometimes defined as a gram-molecular weight. Thus, 



176 



PRACTICAL CHEMISTRY 



a mole of carbon dioxide is 44 grams because the molec- 
ular weight is the mmiber 44. Similarly, a mole of oxy- 
gen is 32 grams, of carbon monoxide is 28 grams, and of 
nitric oxide is 30 grams. 

The volume occupied by one mole of oxygen (at 0° C. 

and 760 mm.) is 22.4 liters. 



Suppose we construct a box 
holding 22.4 liters (Fig. 79) 
and fill it with oxygen (at 
0° C and 760 .mm.), the 
gas will weigh 32 grams. 
This must be so. One liter 
of oxygen weighs 1.43 grams. 
Therefore the volume oc- 
cupied by 32 grams of 
oxygen will be 32 ^ 1.43, 



22.4 
-J LITERS 



Fig. 79. — A box holding i mole or 
22.4 liters of a gas (actual length 
of one edge is 28.2 cm.) 



or 22.4 liters. Simple division shows that i mole of a gas 
occupies 22.4 hters (in round numbers), e.g. carbon mon- 
oxide, 28 -^ 1.25 = 22.4. 

This volume (22.4 liters) is sometimes called the gram- 
molecular volume, since it is the volume of the gram-molec- 
ular weight. It is also called a molar volume, because 
it is the volume of one mole. So it is clear that i mole of 
a gas and 22.4 Hters of the same gas are equal — one being 
the weight and the other the volume of the same mass of gas. 

205. Calculation of molecular weight from a mole. — 
Suppose we construct several cubical boxes each holding 
22.4 liters (Fig. 80), weigh each box, fill each with a gas 
(at 0° C. and 760 mm.), and weigh again. The increase 
in each case is the weight of one mole of the several gases, 
i.e. it is numerically equal to the molecular weight. If 
the gases used, for example, were nitric oxide, carbon mon- 
oxide, hydrogen chloride, and ammonia, the numbers ob- 



MOLECULAR WEIGHTS AND FORMULAS 177 

taincd would be 30, 28, 36.5, and 17. And these numbers 
are the respective molecular weights of these gases. 

Hence to find the molecular weight of a gas by the mole 
method, we fmd the weight of 22.4 Uters of the gas. It 
is not necessary to use such a large volume in the actual 



^ 


y^ 




/ 


y 




^ 


// 




/^ 


y 


22.4 
Liters 


/ 




22.4 

Liters 






22.4 
Liters 






22.4 
Liters 


/ 



.1 

Fig. 80. 



n c I) 

A mole of difTerent gases occupies 22.4 liters. /I = 30 gm. 
NO, 5 = 28 gm. CO, C = 36.5 gm. HCl, D = 17 gm. XH3 

experiment. We simply find the weight of any convenient 
volume and then calculate the weight of 22.4 hters. An 
example will make this clear. If 1.5 liters of carbon mon- 
oxide (at 0° C. and 760 mm.) weigh 1.88 grams, what is 
the molecular weight of the gas? The weight of 22.4 liters 
is found thus: 1.88 -^ 1.5 = 1.25; 1.25 X 22.4 = 28. 
Therefore 28 is the molecular weight of carbon monoxide. 

206. Correct formulas of compounds. — A formula 
of a compound expresses composition. That is, it repre- 
sents by means of symbols the kind and number of atom.s 
in a molecule. 

In 109 it was shown that the simplest formula of a com- 
pound can be calculated from the percentage composition, 
viz. by dividing the per cent of each element in the com- 
pound by the atomic weight, and then, if necessary, re- 
ducing the quotients to the smallest whole numbers. A 
formula thus calculated expresses in the simplest chem- 
ical way the proportions of the different elements in a com- 
pound. But it may not be its correct formula. 

The correct formula of a compound must represent its 
molecular weight. That is, the sum of the weights rep- 



1 78 PRACTICAL CHEMISTRY 

resented by the kind and number of atoms in the formula 
must be equal, or very nearly equal, to the molecular weight 
found by experiment. Let us take an example. A com- 
pound was found by analysis to contain 92.3 per cent of 
carbon and 7.7 of hydrogen, and to have a vapor density 
of 2.4375. Dividing the percentages by the atomic 
weights, we have: 92.3 -^ 12 = 7.7, and 7.7 -^ i = 7.7. 
Since 7.7:7.7 as 1:1, the compound contains at least 
one atom each of carbon and hydrogen, and its simplest 
formula is CH. This formula corresponds to the molec- 
ular weight 13. But the vapor density 2.4375 requires 
the molecular weight 78 {i.e. 2.4375 X 32), which is six 
times the weight (13) corresponding to the formula CH. 
Hence the molecular formula of this compound is not CH, 

but CeHe. 

We recapitulate regarding formulas of compounds : The 
simplest formula of a compound is found by dividing the 
per cent of each element by its atomic weight and reducing 
these quotients to the smallest whole numbers (if neces- 
sary). The molecular formula of a compound is found by 
three steps : (a) Find the simplest formula, (b) divide the 
molecular weight by the sum of the weights of the atoms in 
the simplest formula, (c) multiply the whole numbers of 
the simplest formula by the quotient obtained in (b). 

If the molecular weight of a compound cannot be found by ex- 
periment, then the simplest formula is accepted as the molecular 
formula. For example, a compound contains 40 per cent of calcium, 
1 2 of carbon, and 48 of oxygen. Dividing each per cent by the proper 
atomic weight, we have : 40 -i- 40 = i, 12 -7- 12 = i, 48 -^ 16 = 3. 
That is, one molecule of this compound contains (at least) one atom 
each of calcium and carbon, and three of oxygen; therefore the 
simplest formula is CaCOa- This is also accepted as its molecular 
formula, because the molecular weight cannot be found by any method 
known at present. (See last paragraph in 202.) 



MOLECULAR WEIGHTS AND FORMULAS 179 

207. Molecular formulas of elements. — The molec- 
ular weights of elements, as well as of compounds, can be 
found by experiment (202, 205). Such determinations 
show several interesting facts: 

(i) Several gaseous elements have molecular weights 
which are twice the atomic weight. This means that the 
molecule consists of two atoms, and their molecular for- 
mulas are, for example, O2, Ho, CI2, N2 (also Br2). 

(2) The molecular weights of many metallic elements 
and gaseous elements are identical with their atomic 
weights. This shows that the molecule and atom are iden- 
tical, and the molecular formula is the same as the atomic 
symbol, e.g. Na, K, Zn, Hg, Cd (cadmium), A (argon). He 
(helium), and Ne (neon). Such elements, especially the 
rare gases in the atmosphere, are often called monatomic 
gases to emphasize the fact that their molecules contain only 
one atom. 

(3) Finally the molecular weights of certain elements 
vary with the temperature, decreasing with rise of tempera- 
ture, e.g. at lower temperatures, molecules of iodine, sul- 
phur, and phosphorus are represented by L, Sg, and P4, and 
at higher temperatures by I, S2, and P2. 

208. Molecular equations. — Reactions involving the 
common elementary gases should be expressed by molec- 
ular equations. Thus, the equation for the formation of 
water vapor from hydrogen and oxygen is : — 

2H2 + O2 = 2H2O 

This equation is read thus : Two molecules of hydrogen 
unite with one molecule of oxygen to form two molecules 
of water vapor. Since this equation correctly represents 
the interacting substances as molecules, the equation is 
called a molecular equation. It should be noted that the 



i8o PRACTICAL CHEMISTRY 

proportions by weight are the same as in the simpler or 
gravimetric equation (135, 138). 

Molecular equations are sometimes called volumetric 
equations or gas equations, because they show the 
volumes of gases involved in the reaction. Thus, the 
equation 

H2 + CI2 = 2HCI 
may be written : — 

H2 + CI2 = 2HCI 

I vol. I vol. 2 vol. 

because equal numbers of molecules represent equal vol- 
umes. This equation is read : One volume of hydrogen 
and one volume of chlorine form two volumes of hydro- 
gen chloride. It should be remembered that in molecular 
or volumetric equations a single molecule represents one 
volume of a gas (or vapor) and the coefficient indicates 
the number of volumes. 

EXERCISES 

1. Prepare a summary of molecules and molecular weights. 

2. State and illustrate (a) Gay-Lussac's law and (b) Avogadro's 
theory. 

3. (a) State the argument proving that a molecule of oxygen 
consists of at least two atoms. (&) Apply (a) to nitrogen. 

4. Hydrogen and nitrogen combine in the ratio of 3 to i to form 
2 volumes of ammonia. Show from this relation that a molecule of 
hydrogen contains at least two atoms. 

5. What is the relation between molecular weight and vapor den- 
sity? Illustrate your answer. 

6. Why is the formula of water vapor H2O and not HO or H2O2? 

7. How are the molecular weights of gases determined by (a) the 
vapor density method, and (b) the mole method? 

8. Define and illustrate (a) molecular equation, (b) mole, (c) gram- 
molecular weight, (d) gram-molecular volume. 

9. What is a molecular formula? What is the molecular formula 
of oxygen, nitrogen, chlorine, hydrogen, zinc, mercury, sodium, potas- 
sium, argon, helium? 



MOLECULAR WEIGHTS AND FORMULAS i8r 

10. How is a molecular formula determined? Illustrate. 

11. Express the following as volumetric equations : (a) One volume 
of phosphorus vapor and si.\ volumes of chlorine form four volumes 
of phosphorus trichloride (PClj) vapor; (b) carbon and water (vapor) 
form hydrogen and carbon monoxide. 

12. Topics for review: (a) Gay-Lussac's law (93). (b) Equa- 
tions (Chapter X). (f) Atoms and molecules (101). 

PROBLEMS 

1. 1,000,000 molecules of hydrogen will unite with how many 
molecules of oxygen to form how many molecules of water vapor? 
What will be the relative weights of hydrogen and water vapor? 

2. A liter of sulphurous oxide gas (SO2) weighs 2.9 gm. What is 
the molecular weight of this compound? Compare with the theoretical 
molecular weight. 

3. The vapor density of hydrogen chloride is 1.14. Calculate the 
molecular weight. 

4. If 3000 cc. of a carbon oxide weigh 3.75 gm., what is the molec- 
ular weight, formula, and name ? 

5. Calculate the correct formula of the compound corresponding 
to (a) C = 39.Q, H = 6.7,0 = 53.4, vapor density = 1.906; (b) C = 73-8, 
H = 8.7, X = 17.1, vapor density = 5.03. 

6. What volume of the constituent gases can be obtained by the 
complete decomposition of 6 1. of ammonia? 

7. Write the equation for the reaction between nitric oxide and 
oxygen. What volume of oxygen is needed for 10 1. of nitric oxide? 
What will be the volume of the product? 

8. What is the volume of (a) 2 moles of oxygen, (b) 0.5 mole of 
hydrogen chloride, (c) 22 gm. of carbon dioxide, {d) 22,400 cc. of hy- 
drogen? 

9. The correct formula of a gas is CH4. (a) How many grams 
does a mole weigh? (6) What volume does this weight occupy? 
(c) What is the weight of i 1. of the gas? 

10. A gas contains 69.49 per cent of oxygen and 30.51 of nitrogen, 
(a) What is its simplest formula? (b) If 500 cc. weigh 2.042 gm., 
what is the correct formula? 



CHAPTER XVI 
ATOMIC WEIGHTS 

209. Introduction. — In this chapter we shall study 
the methods of determining atomic weights. But first, 
let us review what we have already learned about atoms 
and atomic weights. In Chapter VII we learned that, 
according to Dalton's atomic theory (100), matter con- 
sists ultimately of particles called atoms, which have the 
same weight if alike but a different weight if different. 
These atoms, furthermore, remain undivided in chemical 
changes. Atoms unite and form molecules. The relative 
weights of atoms are called atomic weights. The standard 
for atomic weights is oxygen = i6. 

210. Determination of approximate atomic weights 
from molecular weights. — The approximate atomic weight 
of an element can be determined from the molecular weights 
of several of its compounds. 

We have seen (202, 205) that the molecular weight of a 
compound can be determined by experiment. After the 
molecular weights of several compounds have been de- 
termined, it is only necessary to find what parts of the 
molecular weights should be chosen as the atomic weight 
of the respective elements that constitute the compounds. 

The steps in this method are : — 

First, determine the molecular weights of several com- 
pounds of an element. 

Second, find by analysis the per cent of the element in 
the compounds. 



ATOMIC WEIGHTS 



183 



Third, find the weight of the element in each molecular 
weight by multiplying the molecular weight l)y the cor- 
responding per cent of the element. 

Fourth, select the minimum value as the approximate 
atomic weight. 

Let us find the atomic weight of carbon by this method. 
The steps are embodied in the accompanying table. 
Column I contains the name of each compound, column 2 



Determixatiox of the Atomic Weight of Carbon 







Per 








Per 






MOL. 


Cent 


Wt. of 




Moi.. 


Cent 


Wt. OF 


Compound 


Wt. 


OF 

Carbon 


Carbon 


Compound 


Wt. 


OF 
CARBO^ 


Carbon 


Carbon Monoxide 


28 


42.9 


12 


Ethylene 


28 


85.7 


24 


Carbon Dioxide 


44 


27.3 


12 


Acetylene 


26 


92.3 


24 


Methane 


16 


75-0 


12 


Ether 


74 


64-9 


48 


Ethane 


30 


80.0 


24 


Propane 


44 


81.8 


36 



the molecular weight, column 3 the per cent of carbon 
in each compound, and column 4 the weight of carbon 
in the corresponding molecular weight. The weights in 
column 4 are found by multiplying the molecular weight 
(in column 2) of the compound (in column i) by the 
corresponding per cent of carbon (in column 3) ; thus 
28 Xo .429 = 12. The minimum value 12 is the atomic 
weight of carbon. 

Obviously, the minimum weight must be the weight of 
a single atom, for it is highly probable that one or more 
compounds in a representative group will contain only 
one atom of a given element ; and the part of the molec- 
ular weight apportioned to this element will of course 
be its atomic weight. In the compounds that contain a 
multiple of this weight, it is likewise obvious that the 



1 84 



PRACTICAL CHEMISTRY 



molecule must contain several atoms of the element. Thus, 
the weight of carbon in ethane is twice that in methane, 
and we conclude that a molecule of ethane contains two 
atoms of carbon — a conclusion in harmony with other 
observations. 

The numerical results obtained by a study of the elements oxygen, 
hydrogen, chlorine, nitrogen, and carbon are summarized in the 
accompanying table. In this table, for the sake of simpHcity, whole 
numbers are used (except in the case of chlorine) and per cents are 
omitted. The minimum weight in each case is the atomic weight of 
the element, e.g. CI = 35.5. 



Determixatiox of Approximate Atomic Weights 







:-i z 


•z, 




H ^ 


^ ^ 


Compound 


Molecular 
Weight 


3 = 5 


2^c 


Weight of 
Chlorine 


1^1 








^ 


2 




* g 


^ u 


Water 


18 


16 


■ — 


— 


Hydrogen Peroxide . 






34 


32 


2 


— 





— ■ 


Hydrogen Chloride . 






36.5 


— ■ 


I 


3S-5 








Ammonia .... 






I '7 


— 


3 


— 


14 


— 


Nitric Acid . . 






63 


48 


I 


— 


14 





Nitrous Oxide . . 






44 


16 


— 


— 


28 





Nitric Oxide . . 






30 


16 


— 


— 


14 





Nitrogen Dioxide . 






46 


32 


— 


— 


14 





Carbon Monoxide 






28 


16 


— 


— 


— 


12 


Carbon Dioxide 






44 


32 


— 


— 


— 


12 


Methane . . . 






16 


— 


4 


— 


— 


12 


Ethylene . . . 






28 


— 


4 


— 


— 


24 


Acetylene . . . 






26 


— 


2 


— 


— 


24 


Ether .... 






74 


16 


10 


— 


— 


48 


Ethyl Alcohol . . 






46 


16 


6 


— 


— 


24 


Chloroform . . 






II9-5 


— 


I 


106.5 


— 


12 


Carbon Tetrachloride 




154 


— 


— 


142 





12 


Cyanogen Chloride . 




61.5 


— 


— 


35.5 


14 
14 


12 

1 

1 


Minimum weight of each element . 


16 


' 


35 5 


1 
12 



This method of determining approximate atomic weights 



ATOMIC WEIGHTS 



was proposed about 1858 by the Italian chemist Canniz- 
zaro (Fig. Si). 

211. Dulong and Petit's law. — Formerly the selection of the 
atomic weights of solid elements, especially metals, was checked by 
an approximate generaliza- 
tion commonly called the 
law of Dulong and Petit, 
which can be stated thus : — 

The atomic weight is the 
quotient of 6.2 j {approxi- 
mately) divided by the specific 
heat. 

As an example we take 
silver. Its specific heat is 
0.057; if 6.25 is divided by 
this number, the quotient is 
about 109. This result shows 
that the atomic weight of 
silver is approximately 109 — 
not 55 or 21S. The exact 
value (found by other meth- 
ods) is 107.88. 

More reliable methods are 

now used in determining 

. , ^ ,^1 1 ^, . FijT. 81. — Cannizzaro (1S26-1010) 

atomic weights, although this * 

so-called law is helpful in deciding between a number and its 

multiple. 

212. Equivalent weights. — The term equivalent urigJits 
rec^uires explanation. Equivalent weights of the elements 
are the weights that are chemically equivalent, provided 
the weights are expressed in terms of the standard for equiv- 
alent weights, viz. 8 grams of oxygen. In other words, 
the equivalent weight of an element is the weight that com- 
bines with or replaces 8 grams of oxygen. For example, 
magnesium and oxygen combine in the ratio of 1.5 to i 
respectively (in round numbers). Now if for the i we 




1 86 PRACTICAL CHEMISTRY 

substitute 8, then the 1.5 becomes 12 ; that is, 12 is the num- 
ber of grams of magnesium that unites with 8 grams of 
oxygen. Therefore 12 is the equivalent weight of mag- 
nesium. Similarly, hydrogen and oxygen combine in the 
ratio of i to 8 ; therefore i is the equivalent weight of hy- 
drogen. 

The equivalent weights of certain elements are not found directly 
in terms of oxygen, but by finding the weight that combines with or 
replaces the equivalent weight of some other element. Thus, chlorine 
and hydrogen combine in the ratio of 35.5 to i ; therefore the equiv- 
alent weight of chlorine is 35.5. Sodium replaces hydrogen from 
water in the ratio of 23 to i ; therefore 23 is the equivalent weight of 
sodium. Again, 32.5 grams of zinc replace i gram of hydrogen 
from hydrochloric acid; therefore 32.5 is the equivalent weight of 
zinc. 

These numbers are sometimes called combining num- 
bers, combining weights, or simply equivalents. The term 
equivalent weights is preferable, because they actually are 
the weights chemically equivalent to each other. Thus, 
if we start with hydrogen chloride (HCl), i gm. of hy- 
drogen — to take a convenient denomination — combines 
with 35.5 gm. of chlorine, and this i gm. of hydrogen can 
be replaced chemically by 32.5 gm. of zinc, 12 gm. of mag- 
nesium, 39 gm. of potassium, or 23 gm. of sodium, and 
so on. These elements are chemically equivalent in the 
ratio of these weights. 

213. The relation of equivalent weights and atomic 
weights. — The equivalent weight of certain elements is 
equal to the atomic weight, e.g. hydrogen, chlorine, and 
sodium. In other cases the atomic weight is a multiple of 
the equivalent weight, e.g. 2 for oxygen, and 3 for alu- 
minium. We say, therefore, that the atomic weight of an 
element is equal to its equivalent weight or a small whole 



ATOMIC WEIGHTS 



187 



multiple of it. This relation is seen in the accompanying 
table {iY\ which approximate weights are used). 

Table of Equivalent Weights and Atomic Weights 



Element 


EQUrVALENT 

Weight 


Atomic Weight 


Multiple 


Oxygen 

Aluminium 

Bromine 

Calcium 

Carbon 

Chlorine 

Hydrogen 

:Magnesium 

Potassium 

Silver 

Sodium 

Sulphur 

Zinc 


8 

9 

80 
20 

3 
35-5 

I 
12 

39 
108 

23 
16 

32.5 


16 
27 
80 
40 
12 

35-5 

I 
24 

39 
108 

23 
32 
65 


2 
2 



The equivalent weight of an element can be very ac- 
curately determined by experiment. Hence if we wish 
to determine the atomic weight accurately, we determine 
the equivalent weight and then multiply it by the correct 
whole number. 

214. Accurate determination of atomic weights. — The 
method of determining atomic weights discussed in 210 in- 
volves finding the vapor density. But since the vapor 
density cannot be found accurately, atomic weights deter- 
mined by the vapor density method have only approximate 
values. The accurate value of an atomic weight is deter- 
mined by painstaking analysis of very carefully purified 
substances. The general method can be illustrated by 
an actual case kindly furnished by the American chemist 
Richards (Fig. 82), who has made exceptionally accurate 
determinations of atomic weights. In determining the 



PRACTICAL CHEMISTRY 



atomic weight of chlorine he found that 28.26299 gm. of 
silver chloride were formed from 21.27143 gm. of silver. 
He accepted AgCl as the formula of silver chloride and 
107.880 as the atomic weight of silver, and calculated the 
atomic weight of chlorine thus : — 

28.26299 — 21.27143 = 6.99156 

\Vt. of : Wt. of : : At wt. of : At. wt. of 

silver chlorine silver chlorine 

21.27143 : 6.99156 : : 107.880 : x 

X = 35-45S 

The international atomic weight (35.46) is based on this 
and other determinations made by this same chemist. 

215. International 
atomic weights. — An in- 
ternational committee se- 
lects the most accurate 
atomic weights of the 
elements. This commit- 
tee selected 16 as the 
atomic weight of oxygen 
(from several values 
formerly used). The 
weights are embodied in 
a table pubUshed at fre- 
quent intervals and called 
the International Table 
of Atomic Weights. The 
Fig. 82. — Richards (1868- ) ^^^j^ -^ g-^.^j^ ^^ ^}^g jn- 

side of the back cover of this book. In this table the 
adopted atomic weights are placed in one column and 
the approximate weights in another. The approximate 
atomic weights are sufhciently accurate for general refer- 




ATOMIC WEIGHTS 189 

ences and in making chemical calculations ; they may 
be used in solving the problems in this book. 

216. Review of methods of determining atomic weights. — The 

methods and principles used in determining the atomic weight of an 
element can be reviewed by following the steps necessary in determin- 
ing the atomic weight of zinc (if its atomic weight were unknown). 

(d) When zinc interacts with dilute hydrochloric acid, hydrogen 
is liberated ; and if a known weight of zinc is used, the weight of zinc 
needed to liberate i gm. of hydrogen is easily calculated. This num- 
ber is the equivalent weight of zinc. Now if one atom of zinc replaces 
one atom of hydrogen, the atomic weight of zinc and the atomic 
weight of hydrogen will have the same ratio as the weight of zinc and 
the weight of hydrogen found by experiment. , According to experi- 
ment the equivalent weight of zinc is about 32.5. This is its relation, 
atom for atom, to hydrogen, and thus far, is its atomic weight. 

(6) When zinc and hydrochloric acid interact, zinc chloride is 
formed. If it is analyzed, the proportion of zinc to chlorine is about 
32.5 to 35.5. Now if the elements combine, atom for atom, the 
atomic weight of zinc is 32.5 (assuming 35.5 as the atomic weight of 
chlorine) . 

(c) However, when zinc is burned in air, zinc oxide is formed. 
If this compound is analyzed, the proportion of zinc to oxygen is 
about 65 to 16. If the elements combine, atom for atom, the atomic 
weight of zinc is about 65 (assuming 16 as the atomic weight of oxy- 
gen). 

(d) According to these three determinations, the atomic weight 
of zinc is 32.5 or 65. We have assumed that the elements unite, atom 
for atom, in each compound. This is an incorrect assumption, be- 
cause an atom of zinc cannot have two different weights — 32.5 and 
65. If the atomic weight is 32.5, zinc oxide must consist of one atom 
of oxygen and two of zinc. But if the atomic weight is 65, zinc chlo- 
ride must consist of two atoms of chlorine and one of zinc, and two 
atoms of hydrogen must have been replaced by one of zinc. 

(e) The molecular weight of zinc* chloride is found by the vapor 
density method to be about 136. Zinc chloride contains 47.8 per cent 
of zinc. Therefore 47.8 per cent of 136, or 65.08, is zinc; that is, 
65.08 is the approximate weight of the smallest part of zinc in zinc 
chloride, and it may be the approximate weight of one atom. If 



iQO PRACTICAL CHEMISTRY 

zinc chloride consists of two atoms of chlorine and one of zinc (weigh- 
ing 65), its molecular weight is about 136. In other words, it is evi- 
dent that our assumption regarding the number of atoms in zinc chlo- 
ride is probably correct. 

(/) We are not absolutely positive, however, that the zinc in a 
molecule of zinc chloride may not be one atom weighing 65, or two 
atoms weighing 32.5 each. But the approximate atomic weight of 
zinc determined by applying the law of specific heats is 66.4 
(i.e. 6.25 -^ 0.094). This shows clearly that the atomic weight of 
zinc is approximately 65 (and not 32.5). 

(g) Accurate analyses of pure zinc compounds show that the 
atomic weight of zinc is 65.37. 

EXERCISES 

1. Prepare a summary showing the relation of atomic weights to 
(a) molecular weights and (b) equivalent weights. 

2. State the three steps in finding atomic weights by the " mini- 
mum weight " method. Illustrate by carbon. 

3. Describe Dulong and Petit's method of finding atomic weights. 

4. What is an equivalent weight? Illustrate by aluminium. 

5. State exactly the meaning of " chemically equivalent." 

6. What is the equivalent weight of (a) oxygen, hydrogen, chlorine, 
carbon, sulphur, bromine, and (b) aluminium, calcium, magnesium, 
potassium, silver, sodium, zinc? 

7. Describe the process of finding an exact atomic weight. 

8. Why is 16 the atomic weight of oxygen? 

9. What is the atomic weight of (a) Al, Ba, Br, Ca, C, CI, Cu, Y, 
Au, H ; [b) I, Fe, Pb, Mg, Mn, Hg, N, O, P, K ; (c) Si, Ag, Na, S, 
Sn, Zn? 

PROBLEMS 

1. If 2 gm. of potassium chloride yield 3.84 gm. of silver chloride, 
calculate the atomic weight of potassium. 

2. If 91.46 gm. of metallic silver, when heated in chlorine, yield 
121.4993 gn^- of pure silver chloride, calculate the atomic weight of 
chlorine. 

3. Calculate the equivalent weights of the respective metals from 
the following data : (a) 0.5 gm. of calcium unites with 0.2 gm. of oxygen 
to form calcium oxide (CaO). (b) 15 gm. of mercury unite with 1.2 gm. 
of oxygen to form mercuric oxide (HgO). 

4. Calculate the equivalent weight of sodium from the following : 



ATOMIC WEIGHTS 191 

(a) 2.3 gm. of sodium liberate o. i gm. of hydrogen from water. 

(b) 1. 15 gm. of sodium liberate 555.5 cc. of hydrogen (at standard 
conditions). 

5. If 0.03 gm. of magnesium yields 30.4 cc. of hydnjgen at 20" C. 
and 750 mm., what is the equivalent weight of magnesium? 

6. Suppose 4.861 1 1 gm. of ferric o.xide (Fe-jOs) yield 3.39995 gm. of 
iron, what is the atomic weight of iron? 

7. If 4.59507 gm. of phosphorus trichloride (PCI.3) give by pre- 
cipitation 14.381 18 gm. of silver chloride, what is the atomic weight 
of phosphorus? 

8. In the synthesis of hydrogen bromide, 0.8606 gm. of hydrogen 
combined with 6S. 25033 gm. of bromine. Calculate the atomic weight 
of bromine. 

9. By experiment, 14.36691 gm. of mercuric bromide (HgBr,) 
yield 14.9694 gm. of silver bromide. Calculate the atomic weight of 
mercury. 

10. Assume that 1.70563 gm. of strontium bromide (SrBrj) require 
1.48707 gm. of silver to precipitate the bromine as AgBr. What is the 
atomic weight of bromine ? 

11. (a) What is the atomic weight of phosphorus, if the specific heat is 
0.189? (b) Of potassium, if the specific heat is 0.166? (c) Of man- 
ganese, if the specific heat is 0.122? (d) Of tin, if the specific heat 
is 0.054? Compmre each with the exact atomic weight. 

12. It was found that 4-58644 gm. of calcium bromide (CaBr>) 
require 4.95025 gm. of silver to precipitate the bromine as AgBr. What 
is the atomic weight of calcium? 



CHAPTER XVII 



VALENCE 



217. What is valence ? — Formulas obtained by the meth- 
ods discussed in Chapter XVI show certain regularities. 
Let us take as examples the following groups : — 

I. Hydrogen Compounds 





HCl HoO 


NH3 


CH4 






HBr HoS 


PH3 


SiH4 






II. Oxi 


ides 






Na20 


CaO AloOs 


SO2 


P2O5 


SO3 


K2O 


MgO P2O3 


CO2 


AS0O5 


Cr03 




III. Acids and Salts 




HCl 


HNO3 


H2SO4 




H3PO4 


NaCl 


NaNOs 


Na2S0, 


I 


Na3P04 


CaClo 


Ca(N03)2 


CaS04 




Ca3(P04)2 


AICI3 


A1(N03)3 


AI2 (804)3 


A1P04 




IV. Bases 







NaOH Ca(0H)2 A1(0H)3 
KOH Ba(0H)2 Bi(0H)3 

These groups might be greatly extended. Careful com- 
parison of these and many other formulas shows two sig- 
nificant facts, (i) Atoms of elements differ in the num- 
ber of atoms or atomic groups of the other elements with 
which they combine. Thus, one atom each of chlorine and 
bromine combines with one of hydrogen ; while one atom 

192 



VALENCE 193 

each of oxygen and sulphur combines with two of hydrogen ; 
and so on. (2) One atom of certain elements unites with 
only one atom or atomic group of certain other elements, 
with only two atoms or two atomic groups of certain others, 
and so on. Thus, one atom of calcium combines with one 
atom of oxygen, two of chlorine, with two NO3 groups, 
one SO4 group, and two OH groups. Hence, we conclude 
that atoms of elements have definite combining capacity. 
The number which expresses the combining capacity of 
an atom of an element is called the valence of the element 
(Table A, 221). 

218. Valence of radicals. — Strictly speaking, valence 
is a property of atoms. But many atomic groups often 
act chemically like individual atoms, e.g. they pass as a 
whole from one compound to another. Hence it is 
customary to assign a valence to atomic groups like SO4, 
NO3, NH4, and OH. Such groups are called radicals 
(163, 179) ; occasionally the term radical is applied by 
analogy to a single atom, e.g. CI in chlorides, C in carbides, 
S in sulphides (as in Table B, 221). In a word, a radical 
has a valence just as an element does. 

219. Valence terms. — An element or radical which 
has the valence i is called a monad ; those w^hich have the 
valence 2 are called dyads; similarly, those elements or 
groups which have the valence 3, 4, 5, 6 are called re- 
spectively triads, tetrads, pentads, and hexads. The cor- 
responding adjectives are univalent, bivalent (or divalent), 
trivalent, quadrivalent (or tetravalent), quinquivalent (or 
pentavalent), and hexavalent. 

220. How valence is represented. - The valence of an 
element or radical may be represented by writing a small 
Roman numeral slightly above the symbol, e.g. U\ O", 
Ar", SO4", OH'. Other ways are given in 226. 



194 



PRACTICAL CHEMISTRY 



221. Tables of valence. — The valence of certain ele- 
ments and radicals is shown in Tables A and B. These 
tables are very useful in writing formulas (225). 



Table A. — Valence of Certain Elements 



Name 


Symbol 


Valence 


Name 


Symbol 


Valence 


Aluminium . 


Al 


3 


Iron (ous) . . 


Fe 


2 


(Ammonium) . 


(NH4) 


I 


Iron (ic) . . . 


Fe 


3 


Antimony (ous) 


Sb 


3 


Lead .... 


Pb 


2 


Antimony (ic) . 


Sb 


5 


Magnesium . . 


Mg 


2 


Arsenic (ous) . 


As 


3 


]\lercury (ous) . 


Hg 


I 


Arsenic (ic) . . 


As 


5 


Mercury (ic) 


Hg 


2 


Barium . . . 


Ba 


2 


Phosphorus (ous) 


P 


3 


Bismuth . . . 


Bi 


3 


Phosphorus (ic) 


P 


5 


Calcium . . . 


Ca 


2 


Potassium . . 


K 


I 


Carbon . . . 


C 


4 


Silicon . . . 


Si 


4 


Copper (ous) . 


Cu 


I 


Silver .... 


Ag 


I 


Copper (ic) . . 


Cu 


2 


Sodium . . . 


Xa 


I 


Gold (ous) . . 


Au 


I 


Tin (ous) . . 


Sn 


2 


Gold (ic) . . . 


Au 


3 


Tin (ic) . . . 


Sn 


4 


Hydrogen . . 


H 


I 


Zinc .... 


Zn 


2 



Table B. — Valence of Certain Radicals 



Group Name 


Symbol 




Group Name 


Symbol 


2: 


OF 


OR 


w 


OF 


or 


a 


COMPOLT«> 


Formula 


< 


Compound 


Formula 


< 
> 


Acetate .... 


C2H3O2 


I 


Iodide 


I 


I 


Bromide . . . . 


Br 


I 


Manganate . . . 


Mn04 


2 


Carbide . . . . 


C 


4 


Nitrate 


NO3 


I 


Carbonate 


CO3 


2 


Nitrite 


NOo 


I 


Carbonate (acid) . 


HCO3 


I 


Oxide 





2 


Chlorate . . . . 


CIO3 


I 


Permanganate . . 


Mn04 


r 


Chloride . . . . 


CI 


I 


Phosphate (ortho) . 


PO4 


3 


Chromate . . . 


Cr04 


2 


Silicate (meta) . . 


Si03 


2 


Dichromate . 


CrsO; 


2 


Sulphate .... 


SO4 


2 


Ferricyanide . . 


Fe(CN)6 


3 


Sulphate (acid) . . 


HSO4 


I 


Ferrocvanide . . 


Fe(CN)6 


4 


Sulphide .... 


S 


2 


Fluoride . . . . 


F 


I 


Sulphite .... 


S03 


2 


Hydroxide . . . 


OH 


I 


Sulphite (acid) . . 


HS03 


I 



VALENCE 195 

For convenience in using or learning the usual valence of certain 
elements and the valence of radicals, the valences given in Tables A 
and B may be rearranged as follows : — 

1. Monads (valence i) — Ag, Au (ous), Br (ide). CI (ide), CIO3, 
Cu (ous), F (ide), H, HCO3, HSO4, Hg (ous), I, K, MnO^ (per), Xa, 
NH4, NO2, NO3, OH. 

2. Dyads (valence 2) — Ba, Ca, CO3, Cr04 ,Cr..07, Cu (ic), Fe (ous), 
Hg (ic), Mg, Mn04 (ate), O, Pb, S (ide), SO3, SO4, SiOs, Sn (ous), Zn. 

3. Triads (valence 3) — Al, As (ous), Au (ic), Bi. Fe (ic), Fe(CN)6 
(i). P (ous), PO4, Sb (ous). 

4. Tetrads (valence 4) — C, C (ide), Fe(CN)6 (o). Si, Sn (ic). 

5. Pentads (valence 5) — As (ic), P (ic), Sb (ic). 

222. Variable valence. — Most elements and radicals have a 
fixed valence. But the valence of some elements varies with the 
combining element and the conditions under which the combination 
occurred. For example, iron, copper, mercury, and a few other ele- 
ments form two series of compounds in which these elements have a 
different valence. These series are designated as -ous and -ic (see 
502). Thus, iron forms ierrous compounds {e.g. ferrous sulphate) in 
which iron has the valence 2, and ferr/c compounds {e.g. ferric chloride) 
in which iron has the valence 3. (See 228.) 

223. Interpretation of valence by combination. — Ele- 
ments which have the same valence combine with each other 
unit for unit. This is a general rule. For example, sodium 
and chlorine each has the valence i ; hence one atom of 
sodium combines with one atom of chlorine to form one 
molecule of sodium chloride (NaCl). 

Elements which have a different valence usually com- 
bine with each other so that the total valence of the atoms 
of each element in a molecule is equal. This is also a gen- 
eral rule. In other words, the valence of the two parts 
must balance. For example, two atoms of hydrogen (each 
having the valence i) combine with one of oxygen (having 
the valence 2) to form one molecule of water (HoO) ; sim- 
ilarly two atoms of aluminium (each having the valence 3) 



196 PRACTICAL CHEMISTRY 

combine with three atoms of oxygen (each having the va- 
lence 2) to form one molecule of aluminium oxide (AI2O3). 
The two rules just given apply to radicals. Thus, am- 
monium and hydroxyl each has the valence i ; so one NH4 
radical combines with one OH radical to form one molecule 
of ammonium hydroxide (NH4OH). Similarly, two NH4 
radicals combine with one S4O radical (having the valence 2) 
to form one molecule of ammonium sulphate ((NH4)2S04). 
So also, three atoms of calcium (each having the valence 2) 
combine with two PO4 radicals (having the valence 3) to 
form one molecule of calcium phosphate (Ca3(P04^'2)- 

224. Interpretation of valence by displacement or sub- 
stitution. — ■ Just as atoms and radicals of the same valence 
combine, unit for unit, and those of different valence combine 
so that the valence of the two parts (element or radical) 
balances, so also atoms and radicals displace each other 
— unit for unit if the valence is the same, or equivalently 
if the valence is different. Let us take several examples : 
(i) When silver displaces hydrogen in hydrochloric acid, 
one atom of silver (having the valence i) displaces one 
atom of hydrogen (having the valence i), thereby forming 
silver chloride (AgCl). (2) Similarly, one atom of chlorine 
(having the valence i) displaces one OH radical (having 
the valence i) from sodium hydroxide, thus producing 
sodium chloride (NaCl). (3) So also, when aluminium 
is substituted for the hydrogen in sulphuric acid, two atoms 
of aluminium (each having the valence 3) are needed to 
balance the three SO4 radicals (each having the valence 2) 
in the aluminium sulphate (Alo(S04)3) formed. 

225. Writing formulas from valence. — Formulas of 
many compounds may be written by using the tables of 
valence. 

(i) Suppose we wish to write the formula of 



VALENCE 197 

J'rom 'ra])le A the valence of mag- 
nesium is found to be 2, and from Table B the valence 
of chlorine in chlorides is found to bei. Remembering 
the fnndamcntal rule that in most compounds the total 
valence of each of the two parts must be equal, it is clear 
that the formula must contain one atom of magnesium 
and two atoms of chlorine ; hence the formula is MgCb. 

(2) Suppose we wish to know the formula of lead 
nitrate. From the tables, the valence of lead is 2 and of 
the NO3 radical is i ; so it is necessary to have two XO3 
radicals for one atom of lead ; the formula, therefore, is 

Pb(X03)2. 

(3) Similarly, the formula of aluminium oxide is 
AI2O3, because 2 and 3 are the least number of atoms 
of Al and which give a balanced valence (6 in each case). 

Formulas of salts are frequently needed. These can 
be readily wTitten by learning the formulas of the common 
acids and substituting the correct number of atoms for the 
hydrogen. Thus, the formula of sulphuric acid is H0SO4. 
Therefore, all sulphates will have one or more SO4 radicals 
as one part of the formula and one or more atoms of a metal 
for the other part. If the metal has the valence of i, the 
formula will contain two atoms of the metal, e.g. Xa2S04, 
K2SO4. Ag2S04; if the valence is 2, there will be only one 
atom, e.g. CaS04, BaS04, CUSO4. Whereas if the valence 
is 3, there will be two atoms of the metal and three SO4 
radicals, e.g. AI2 (504)3. Similarly, all nitrates have NO3 
(one or more), all chlorides have CI (one or more), all phos- 
phates have PO4 (one or more), and so on. It is not neces- 
sary to learn by heart formulas of salts ; they can be written 
by applying the valence rules. 

226. Representation of valence. — The valence of elements and 
radicals may be represented in various ways. One has already been 



igS PRACTICAL CHEMISTRY 

given, viz. H\ O", PO4'". Sometimes short lines are used, e.g. H — , 
= , — O — , Al =, etc. If lines are used to represent valence in com- 
pounds, a single line answers for two elements. Thus, the formula 

of water is written H — O — -H rather than H — — O H. Simi- 

/H OH 

larly, ammonia gas is N^H and calcium hydroxide is Ca<( or 

\H \0H 

,0— H 
Ca<^ . Such formulas are called structural or graphic formulas, 

^O— H 
for they show the probable arrangement of the atoms in the mole- 
cules. Thus, the graphic formula of nitric acid is usually written 

H— — N.^' , because this arrangement of atoms not onlv shows 

^O 
the correct valence of each element but it also represents certain 
facts about nitric acid, e.g. that the hydrogen is not combined di- 
rectly with nitrogen. Structural formulas are useful, especially in 
organic chemistry (Chapter XXIII), but it must not be forgotten 
that they are merely representations ; the lines are intended to in- 
dicate the numerical value of the valence and not the strength of the 
combination of the atoms. 

227. Determination of valence from atomic and equiv- 
alent weights. — We learned in 213 that the atomic 
weight is equal to the equivalent weight or is a small whole 
multiple of it. The number (i or a small multiple) ex- 
pressing the relation of the atomic and equivalent weight 
of an element is the valence. Hence the valence of an element 
is found by dividing its atomic weight by its equivalent 
weight, that is: — 

Valence = Atomic Weight -=- Equivalent Weight 
Thus, the atomic weight of magnesium is 24, and its equiv- 
alent weight is 12. Therefore the valence is 24 ^ 12, 
or 2. 

228. Exceptional compounds. — The formulas of certain com- 
pounds apparently do not conform to the simplified conception of 
valence discussed above. Carbon monoxide (CO), calcium carbide 



\aij:xck 199 

(CaC-i), lead tctroxidc (Pb304), magnetic iron oxide (Fe304), hydrogen 
peroxide (H2O2), acetylene (C2H2),and ethylene (C2H4) are apparent 
exceptions. Interpretations of these apparent exceptions must be 
sought in a larger textbook. (See, however, 503, 573.) 

229. Importance of valence. — Valence is very useful 
in writing formulas and in understanding analogous com- 
pounds. The valence of the common elements and radicals 
should be learned and used. (See especially Exercises 
1, 3, 4, 8, 9, below.) 

EXERCISES 

1. What is the valence of these elements and radicals? (a) H, 
O, C, CI; {b) Ag, K, Na, NH4; (c) NO3, OH; (d) Ba, Ca, Cu, 
Fe (ous), Mg, Pb, Zn ; (e) CO3, SO4, S (ide) ; (/) Al, Fe (ic), PO4. 

2. State the fundamental rule for writing formulas from valence. 

3. Write the formula of the chloride of potassium, sodium, silver, 
copper (ous), copper (ic), mercury (ous), mercury (ic), iron (ous), 
iron (ic), zinc, tin (ous), tin (ic), calcium, barium, magnesium, bismuth, 
aluminium, ammonium, lead. 

4. Write the formula of the sulphate of K, Xa, Ag, Cu, Fe (ous), 
Zn, Pb, Ca, Ba, Mg, Cr, Al, NH4. 

5. Write the formula of the following compounds and indicate 
the valence of each element or radical by Roman numerals : ammonium 
fluoride, sodium silicate, potassium manganate, barium phosphate, 
zinc iodide, ammonium chromate, silver chromate, magnesium oxide, 
sodium dichromate, aluminium chloride, ferrous bromide, calcium phos- 
phate, mercurous nitrate. 

6. Write the formulas of the following (as in Exercise 5) : ferrous 
carbonate, aluminium phosphate, calcium fluoride, sodium perman- 
ganate, phosphoric acid, silicic acid, sulphurous acid, nitrous acid, 
chromic acid, hydriodic acid, carbonic acid. 

7. Define and illustrate the term eqiiivaleni weight. What is the 
equivalent weight of hydrogen, oxygen, sulphur, zinc, copper, magne- 
sium, silver, potassium, aluminium? State the relation of each to its 
atomic weight. 

8. Write the formula of the nitrate of calcium, silver, iron (ic), 
mercury (ous), barium, magnesium, aluminium. 

9. Write the formula of the oxide of Al, Sb (ous and ic). As (ous 
and ic), Ba, Bi, Ca. 



200 PRACTICAL CHEAIISTRY 

10. Write the formula of (a) the carbonate of Cu (ic), Ba, Ag; 

(b) the iodide of Hg (ous and ic), Pb, Ag, Xa, Fe (ous and ic), Al ; 

(c) the chlorate of Xa, Ba, Ag. 

11. Write the formula of (a) the dichromate of Pb, Xa, Al, Ag ; 
(b) the manganate of Xa, Ca, Ag ; (c) the nitrate of Pb, Ca, Cu (ous 
and ic). 

12. Write the formula of (a) the nitrite of Xa, Ca, Pb, Cu (ic) ; 
{b) the permanganate of Xa, Ag, H, K; (c) the sulphate, chloride, 
nitrate, carbonate, sulphite, bromide of H. 



CHAPTER XVni 
IONS AND IONIZATION 

230. Introduction. — Many properties of solutions and 
the general properties of acids, bases, and salts have al- 
ready been enumerated (161-165). Considerable atten- 
tion has also been given to examples of acids, bases, and 
salts, viz. hydrochloric and nitric acids, ammonium hydrox- 
ide, and chlorides and nitrates. In this chapter we shall 
consider more in detail the properties of dilute solutions of 
acids, bases, and salts. 

231. Theory of ionization. — Solutions of acids, bases, 
and salts differ conspicuously in certain properties from 
solutions of other substances {e.g. sugar, glycerin, alcohol). 
That is, we have two classes of solutions. One class — 
acids, bases, and salts — is active chemically, conducts an 
electric current, and behaves abnormally when boiled or 
frozen. Whereas the other class — not acidic, basic, or 
salty — is not active chemically, does not conduct an elec- 
tric current, and behaves normally when boiled or frozen. 

The properties of solutions, especially solutions of acids, 
bases, and salts, are explained more or less acceptably by 
the theory of ionization, which was proposed in 1887 ^Y 
the Swedish chemist Arrhenius (Fig. 83). We shall state 
and explain the theory first, and then show how the theory 
helps us understand the properties of dilute solutions of 
acids, bases, and salts. The theory is usually stated as 
follows : — 



202 



I'k \(l I( \L CIII'lMISrRY 



Adtis, hdsrs. It 11(1 SiiHs, icl/cfi dissolved in Kuihr, d(r(f)n/>()sc 

into /xirlidcs ( //tiri^nl u'/7// clcilriiily. 

'This tlu'ory humus ihat ;i solution of sodium chloride, 

lor cxaiupk', (.onsisls of water lhrouu;hout which arc dis- 
tributed souu' molecules 
of sodium ( hloridc to- 
gether with particles of 
electrically charged so- 
dium and chlorine into 
which the other mole- 
cules of sodium chloride 
ba\'e dissociated. 

232. What are ions? 
- — The decomj)osition, or 
dissociation, of acids, 
bases, and salts when in 
solution is called ioniza- 
tion. The electrically 
charged particles formed 
bv ionization are called 

Fig S^,. ArrluMuus (.850- ) .^^^g j^^^,j^ j^^,^ j^ .^ ^^^^^_ 

tion of a molecule. Two kinds of ions are present in 
every electrolytic solution, viz. electro-positive ions, or 
cations, and elect ro-negatixe ions, or anions. 

K>ns, although formed by the dissociation of molecules, 
must not be confused with atoms. /^);/.s~ arc electrically 
charged atoms or radicals. The c>lectric charge changes the 
atom or radical, so that the properties of ions are quite 
tlitlerent from those of atoms. For example, in a solution 
of sodium chloride the electro-positive sodium ions move 
abcHit in the water witlunit producing any apjKirent chemical 
change ; whereas ordinary sodium interacts violently with 
water, as we have already seen (49). Similarly, the chloride 




IONS AND IONIZATION 203 

ions circulate freely in wdter and exhibit none of the effects 
of chlorine on water (145, 146 ^ It must be understood 
that the electric charges on the ions in a solution do not 
come from the electricity that may subsequently be passed 
through the solution. The ions are electrically charged just 
as soon as the molecules decompose in the solution (238). 

233. How ions are represented. — Ions are represented 
by chemical symbols supplemented by the sign that desig- 
nates the kind and amount of the electric charge. Thus, the 
ions formed by sodium chloride are Na+ and Cl~. In 
sodium chloride solution a molecule of sodium chloride dis- 
sociates into one ion each of sodium and chlorine. Hence 
the number of sodium ions equals the number of chloride 
ions ; and the sum of the positive charges on all the sodium 
ions equals the sum of the negative charges on all the chlo- 
ride ions. 

On the other hand in calcium chloride solution (CaClo), 
each molecule dissociates into two chloride ions and one 
calcium ion. Hence the ions formed by the dissociation 
of calcium chloride are designated Ca++ and 2C1~ {not Cl2~)* 

Since the sum of each kind of electric charge must be 
equal {i.e. the total positive equals the total negative), the 
charge on each calcium ion must be twice the charge 
on each chloride ion. Similarly, the ions formed by cal- 
cium hydroxide (Ca(0H)2) are Ca++ and 2OH-, and by 
calcium sulphate are Ca^^ and S04~ ~. 

In ordinary chemical formulas, atoms and radicals are 
represented as united, e.g. Cl-2, CaClo, Ca(0H)2. But when 
the molecule dissociates, independent particles (ions) are 
formed. Therefore we represent ions as separate particles. 
That is, the Clo in CaClo becomes 2CI- or Ch -h Ch, but 
not Cl2~. 

234. A new definition of acid and base. — Specitic prop- 



204 PRACTICAL CHEMISTRY 

erties are exhibited by solutions of typical acids and bases. 
Thus, acids have a sour taste and turn Utmus red ; bases 
have a bitter taste and turn htmus blue. When these 
properties are interpreted by the theory of ionization, in- 
teresting and important conclusions result. Acids, bases, 
and salts are electrolytes. Hence their solutions contain 
ions, and the properties of such solutions are ascribed to the 
ions. According to the theory of ionization, then, an acid 
is a compound whose solution contains hydrogen ions (H+) , 
while a base is a compound whose solution contains hy- 
droxyl ions (0H-). These definitions should be compared 
with those previously given (161-165) . 

235. Salts and ionization. — Salts may be defined in 
several ways. For example, they are compounds (other 
than water) resulting from neutralization of acids and bases. 
Again, they are formed by substituting (i) a metal for the 
hydrogen of an acid or (2) a non-metal for the hydroxy 1 of 
abase (163-165). 

According to the theory of ionization, salts may be de- 
fined in two ways. First, salts are electrolytes which in 
solution yield neither hydrogen nor hydroxyl ions. Second, 
salts are compounds finally formed by the union of the posi- 
tive ion of a base and the negative ion of an acid. Later we 
shall study different kinds of salts. (See 273, 293.) 

236. A new definition of neutralization. — In 164 we 
saw that neutralization is a chemical change in which 
an acid and a base interact and form a salt and water. 
Neutralization, interpreted by the theory of ionization, is 
the combining of hydrogen and hydroxyl ions to form 
molecules of water. Suppose solutions of hydrochloric 
acid and potassium hydroxide are mixed in the proper 
proportions. The mixture at first contains ions of hydro- 
gen, chlorine, potassium, and hydroxyl. But the hydrogen 



IONS AND lONI/A'I ION 205 

and hydroxyl ions immediately unite to form molecules 
of water, because water does not dissociate to any appre- 
ciable extent. The final solution is thus rendered neutral 
by the removal of the hydrogen and the hydroxy] ions — 
the acidic and basic constituents respectively. 

The ionic equation expressing the neutralization of po- 
tassium hydroxide by hydrochloric acid is : — 

K+ + OH- + H+ + CI- = K+ + CI- -f- HoO 

The potassium and chloride ions move freely about in the 
solution. If the solution is evaporated, the ions unite as 
it becomes concentrated until nothing remains except the 
neutral salt potassium chloride. Since neutralization is 
the combining of hydrogen and hydroxyl ions to form 
water, the gen^^ral ionic equation for neutralization is : — 

H+ -f OH- = H,0 

Hj'drogen Ion Hydroxyl Ion Water 

237. Interpretation of certain facts by the theory of 
ionization. — ■ The theory of ionization, like other theories, 
must meet one important requirement, i.e. it must explain 
facts derived from experiment. We shall now interpret 
certain facts by this theory. 

238. Behavior of solutions toward an electric current. — 
Water itself conducts electricity very slightly indeed. If 
solutions are subjected to the action of an electric current, 
the results vary. Solutions of some substances do not 
conduct electricity. Whereas solutions of certain sub- 
stances conduct electricity readily ; these substances are 
acids, bases, and salts. 

A simple experiment enables us to find out what substances arc 
electrolytes and what are non-electrolytes, i.e. what substances form 
conducting solutions and what form non-conducting. The appa- 
ratus is shown in Fig. 84. It consists of a beaker .1 containing the 



2o6 



PRACTICAL CHEMISTRY 




solution, into which clip two pieces of platinum, B and C, called elec- 
trodes, through which the current enters and leaves the solution. 
The wire from the electrode C and the wire E from the electric light 
bulb D are connected with the electric light system. The wire from 

the electrode B is also connected with 
the electric light bulb D. When 
the current is turned on, the bulb 
glows if the solution contains an 
electrolyte. For example, if solu- 
tions of hydrochloric acid, sodium 
hydroxide, and calcium chloride are 
Fig. 84. — Apparatus for show- tried in succession, the bulb glows 
ing that only solutions of bj-ightlv. But the bulb does not 
acids, bases, and salts con- ^^^^^^ ■( gQi^^io^s ^f ^^gar, alcohol, 

duct an electric current , . , 

or glycerm are used. 

Thus we see that only solutions of acids, bases, and salts 
are electrolytes. This fact is readily interpreted by the 
theory of ionization. Solutions of acids, bases, and salts, 
according to the theory, contain electrically charged par- 
ticles—ions. Whereas solutions of other substances do 
not. Hence, when an electric current is introduced into 
solutions of acids, bases, or salts, particles already charged 
with electricity are there to conduct the current. No such 
particles are in solutions of other substances ; hence such 
solutions cannot conduct an electric current. 

239. Chemical reactions in solutions of acids, bases, 
and salts. — Dry potassium chloride and dry silver ni- 
trate do not interact chemically, but if their solutions are 
mixed, a precipitate of silver chloride is immediately pro- 
duced. Furthermore, any dissolved chloride will interact 
in the same way with silver nitrate or any soluble silver 
salt. 

Let us interpret this fact by the theory of ionization. 
Solutions of potassium chloride and silver nitrate contain 
potassium ions (K+). chloride ions (CI"), silver ions (Ag+), 



IONS AND IONIZATION 207 

and nitrate ions (XOa"). Now when certain ions are in- 
troduced into the same solution, they react chemically. 
Thus, silver ions and chloride ions, if brought into the same 
solution, always combine to form insoluble silver chloride ; 
and this precipitate serves as evidence of the chemical 
change. According to the theory, the source of the silver 
ions and the chloride ions is immaterial. And it is a fact 
that hydrochloric acid and solutions of different chlorides 
precipitate silver chloride from a solution containing sil- 
ver ions, whether the silver ions are furnished by silver ni- 
trate, silver sulphate, or any other soluble silver salt. This 
is the explanation offered by the theory of ionization for 
the precipitation of silver chloride, which you will recall 
is the usual test for hydrochloric acid and all soluble 
chlorides (160). The test is a test for ions (Cl~ and Ag+). 
The ordinary equation for this test is : — 

HCl -f AgNGs = AgCl + HXO3 

The corresponding ionic equation is : — 

H+ + CI- + Ag+ + NO3- = AgCl + H+ -f XO3- 

A general form of this equation is : — 

CI- + Ag+ = AgCl 

On the other hand, substances quite similar in name and 
related in composition do not react alike. Thus, no chemi- 
cal action is observed when solutions of potassium chlorate 
and silver nitrate are mixed, despite the fact that the solu- 
tions contain ions and that chlorine is a constituent of po- 
tassium chlorate. This apparent contradiction is readily 
explained by the theory. Potassium chlorate solution 
contains potassium ions (K+) and chlorate ions (CIO3-), 
and w^hen silver nitrate solution is added, the solution con- 



2o8 PRACTICAL CHEMISTRY 

tains two more kinds of ions — silver ions (Ag+), and nitrate 
ions (NOs"). But compounds which might be formed by 
the various combinations of these ions are soluble. Hence 
the ions remain uncombined, for the most part, in the solu- 
tion. Silver nitrate is effective in testing for chlorine com- 
pounds which yield chloride ions but not for other chlorine 
compounds, such as potassium chlorate (KCIO3). 

Similarly, the test for sulphuric acid and all soluble 
sulphates is the formation of insoluble barium sulphate 
(BaSO^) upon the addition of a solution of barium chloride 
or any other soluble barium compound. Sulphuric acid 
and sulphate solutions contain sulphate ions (S04~ ~) , which 
combine with barium ions (Ba++) furnished by the soluble 
barium compound. But this test is not apphcable to other 
sulphur compounds, such as sulphides, sulphites, and thio- 
sulphates, because solutions of these sulphur compounds 
do not contain sulphate ions. The ionic equation for the 
usual test for a sulphate is : — 

Ba++ + 2CI- + 2H+ + SO4-- = BaS04 + 2CI- + 2H+ 

In the laboratory many of our common tests involving acids, 
bases, and salts are ionic reactions, i.e. reactions in which certain ions 
formed by dissociation reunite into a precipitate. 

240. Electrolysis. — The simple experiments with solu- 
tions of acids, bases, and salts described in 238 (in which 
the bulb glowed) are examples of electrolysis. Electrolysis 
is the term apphed to the series of changes accompanying 
the passage of an electric current through a solution of an 
acid, base, or salt. The facts connected with electrolysis 
can be adequately interpreted by the theory of ionization. 

If hydrochloric acid is put in the Hofmann apparatus 
(provided with carbon instead of platinum electrodes), 
and an electric current is passed through the acid, bubbles 



IONS AND IONIZATION 



209 



of gas rise from each electrode — hydrogen from one and 
chlorine from the other. 

Let us interpret this example of electrolysis l)y the theory 
of ionization. 

(i) The solution of hydrochloric acid contains hydrogen 
chloride molecules, hydro- . . 



\^ 



Fig. 85. — Sketch to illustrate the 
electrolysis of hydrochloric acid 



gen ions (H+), and chloride 
ions (CI"). These ions are 
in the solution before the 
electric current is turned on. 

(2) When the electric 
current is turned on, the 
electrodes become charged 
with electricity — the anode positively ( + ) and the cath- 
ode negatively (— ). 

(3) According to an old principle, bodies charged with 
the same kind {e.g. plus) of electricity repel each other ; 
whereas bodies charged with different kinds {i.e. plus and 
minus) attract each other. In other words, the negative 
electrode (cathode) attracts the positive ions (cations) 
and repels the negative ions (anions). At the same time the 
positive electrode (anode) attracts the negative ions (anions) 
and repels the positive ions (cations). As a result of this 
attraction and repulsion the ions actually move toward 
the electrodes and, of course, carry their electric charges with 
them. Anions go to the anode and cations to the cathode. 

In this case, hydrogen ions (H+) go to the cathode and 
chloride ions (C1-) go to the anode (Fig. 85). This migra- 
tion of ions, as it is called, was first studied carefully by the 
EngUsh scientist Faraday (Fig. 86), who named the charged 
particle " ion " from a Greek word meaning wanderer. 
The term ion thus emphasizes the fact that in an electro- 
lytic solution the charged particles move about ; when the 



2IO 



PRACTICAL CHEMISTRY 



current of electricity is passed through the solution, these 
movements are regulated, so to speak, negative ions mi- 
grating to the positive electrode and positive ions to 
the negative electrode. 

(4) As soon as the ions come in contact with their re- 
spective electrodes they 
act in accordance with 
another long-established 
principle ; that is, they 
lose their electric charges. 
In other words, when the 
positive ions, or cations 
(H+), touch the cathode, 
the electric charges on 
the ions are neutralized. 
Electric charges, equal in 
quantity, but opposite 
in kind, are lost by the 
cathode ; but are con- 
stantly renewed by the 
Fig. 86. - Faraday (1791-1867) battery or dynamo. The 

hydrogen ions (H+) once deprived of their electric charges 
do not regain them but immediately become ordinary, 
uncharged hydrogen atoms (H) which combine and 
escape as molecules of hydrogen gas (H2). Similarly, 
the negative ions, or anions (CI"), migrate to the anode, 
lose theit charges, become chlorine atoms (CI), and escape 
as chlorine gas (CL). As a final result of the electrolysis 
of hydrochloric acid, hydrogen and chlorine are the sole 
products. 

241. Electrolysis sometimes yields secondary prod- 
ucts. — When a solution of sodium hydroxide undergoes 
electrolysis, hydrogen is liberated at the cathode and oxygen 




IONS AND IONIZATION 211 

at the anode. The electrolysis proceeds as usual, the 
cations (sodium ions — Na+) migrate to the cathode and 
the anions (hydroxy 1 ions — 0H~) to the anode. As the ions 
are discharged, chemical changes take place. The sodium 
atoms (Na) which are produced at the cathode, react with 
the water (in the solution), forming hydrogen and sodium 
hydroxide. The unstable hydroxyl radicals (OH) which are 
produced at the anode break down into oxygen (O2) and 
water (H2O). Hence the final result is the production of 
two secondary products, viz. hydrogen at the cathode and 
oxygen at the anode. We might summarize the process as 
follows : — 

(i) Ionization, NaOH = Na+ + OH- 

(2) At the cathode, 2Na + 2H0O = H2 + 2XaOH 

(3) At the anode, 4OH = O2 + 2H2O 

The electrolysis of copper sulphate adds one more point. 
In a copper sulphate solution the ions are copper ions (Cu^+) 
and sulphate ions (S04~~). When the electric current 
is passed through the solution, the copper ions (Cu++) mi- 
grate to the cathode, lose their electric charges, become 
copper atoms (Cu), and adhere as metallic copper to the 
cathode. The sulphate ions (S04~~) lose their electric 
charges at the anode and immediately interact with the 
water around the anode, forming sulphuric acid (H2SO4) 
and oxygen atoms (O), which unite into molecules (O2) and 
escape from the solution as a gas. But the sulphuric acid 
mingles with the solution and dissociates into its ions, and 
continues to participate in the process. 

The so-called electrolysis of water (88) is interpreted as follows: 
Water itself does not conduct electricity to an extent which is com- 
parable with the behavior of an electrolytic solution, because water 
dissociates only inappreciably and therefore gives only an exceedingly 



212 PRACTICAL CHEMISTRY 

small number of ions. However, if sulphuric acid is added, the solu- 
tion will be provided with hydrogen ions (H+) and sulphate ions 
(S04"~~). When an electric current is passed through this solution, 
hydrogen ions migrate to the cathode, lose their electric charges, 
become hydrogen atoms (H) and escape as hydrogen gas (Ho). The 
SO4 ions migrate to the anode, lose their electric charges, and interact 
wdth the water to form sulphuric acid and oxygen. The oxygen (Oo) 
escapes as a gas, while the sulphuric acid continues to play the usual 
part in the process. 

After the electrolysis has proceeded some time, the solution will 
be found to contain the same weight of sulphuric acid but less water — 
in fact, the decrease in the weight of water equals the weight of the 
liberated gases. 

242. Another definition of electrolysis. — We may now 
re-define or describe electrolysis as ionic migration 
induced by the electric current, the ions moving to their 
respective electrodes, where they are transformed into 
atoms or radicals which escape wholly or in part as ele- 
ments, or which form various products by interaction with 
the water of the solution. 

243. Practical applications of electrolysis. — Electrotyping and 
electroplating consist in depositing a thin film of metal upon a surface. 
The process of electrotyping is substantially as follows : The page of 
type, for example, is first reproduced in wax. This exact impression 
is next covered with powdered graphite to make it conduct electricity. 
The coated mold is then suspended as the cathode in an acid solution 
of copper sulphate; the anode is a plate or bar of copper. When 
the electric current is passed through the solution, electrolysis occurs, 
and copper is deposited upon the mold in a film of any desired thick- 
ness. The exact copper copy is stripped from the mold, backed with 
metal, and used instead of the type for printing. The process of 
electroplating differs from electrotyping in only one essential, viz. in 
electroplating the deposited film is not removed from the object. 

244. Boiling and freezing points of solutions. — Solu- 
tions boil at a higher temperature and freeze at a lower 
temperature than water. When i mole (i.e. the number of 



IONS AND IONIZATION 213 

grams numerically equal to the molecular weight — 204) 
of a non-electrolyte, such as alcohol, is dissolved in 
1000 grams of water, the boiling point is raised from 100° C. 
to 100.52° C, and the freezing point is lowered from 0° C. 
to —1.86° C. Whereas when solutions of electrolytes, 
i.e. acids, bases, and salts, are experimented with, the 
boiling point is higher and the freezing point is lower than 
that produced by non-electrolytes under parallel condi- 
tions. Thus, I mole of sodium chloride will cause a change 
in temperature nearly twice that produced by alcohol. 
Solutions of all electrolytes behave in the same way, though 
they differ in the amount of change. To sum up the re- 
sults of experiments, we may say that acids, bases, and 
salts cause abnormal raising of the boiling point and ab- 
normal lowering of the freezing point. 

According to the theory of ionization, solutions of non- 
electrolytes contain only molecules, while solutions of elec- 
trolytes contain molecules and ions — the number of 
particles depending on the substance and the concentration 
of the solution. Hence the number of particles (molecules 
and ions) moving about freely in the electrolytic solution 
is greater than in the non-electrolytic solution. Ions have 
the same effect as molecules on the boiling and freezing 
points of a solution. Hence the greater the number of 
particles the greater should be the raising of the boihng 
point and the lowering of the freezing point. This is the 
fact. In other words, the theory of ionization furnishes 
an acceptable explanation of the abnormal boiling and 
freezing points of solutions of acids, bases, and salts. 

The agreement between fact and theory is still further 
confirmed when molecular weights are determined by the 
freezing point or the boiling point method — a method too 
complicated to explain here. It is found that the molec- 



214 



PRACTICAL CHEMISTRY 



ular weights of non-electrolytes agree with the values found 
by other methods, whereas in the case of electrolytes 
(i.e. acids, bases, and salts), not only do the values dis- 
agree with those found by other methods but the values 
also vary with the concentration of the solution. 

245. What ions are in a solution? — ^ As a rule, the ions 
formed by an electrolyte are the charged atom or group 
corresponding to the two parts of the compound. Thus, 
nitric acid consists of the two parts H and NO3, and the 
ions are H+ and NO3-. Similarly, the parts of sodium hy- 
droxide are Na and OH, and the ions are Na+ and OH". 

The ions normally formed by the ionization of acids, 
bases, and salts are given in the accompanying table of 
ions. 

Table of Ions 



Element 

OR 
RADICAL 



Ammonium 
H3^drogen . 
Mercury (ous) 
Potassium 
Silver . 
Sodium . 
Bromide 
Chlorate 
Chloride 
Hydroxy! 
Iodide . 
Nitrate . 



Ion 



NH4^ 
H+ 
Hg+ 
K+ 

Ag+ 
Na+ 
Br- 
CIO3- 

ci- 

OH- 

I- 

NO3- 



Element 

OR 
RADICAL 



Barium . 
Calcium 
Copper . 
Iron (ous) 
Lead 

Magnesium 
jNIercury (ic) 
Tin (ous) . 
Zinc . 
Carbonate . 
Chromate . 
Bichromate 
Sulphate 
Sulphide 



Ion 



Ba++ 

Ca++ 

Cu++ 

Fe++ 

Pb++ 

Mg++ 

Hs++ 

Sn++ 

Zn++ 

CO3- - 

Cr04- 

CroOy" 

SO4- - 

S-- 



Element 

OR 

Radical 



Aluminium 
Antimony 
Bismuth . 
Iron (ic) . 



Tin (ic) 



Ion 



AI+++ 

Sb+++ 
Bi+++ 



Sn- 



246. What electric charges are on ions ? — As repeatedly 
stated, certain ions (cations) carry a positive charge and 
others (anions) a negative charge. These can be selected, 



IONS AND IONIZATION 215 

of course, from the table of ions. It is convenient, however, 
to remember these simple rules regarding the kind of 
charge : — 

(i) Hydrogen and metals form positive ions or cations 
{e.g. H+, Cu++). 

(2) Non-metals — except hydrogen — form negative ions 
or anions {e.g. Cl~). 

(3) Characteristic radicals of electrolytes form negative 
ions or anions {e.g. NOs", SOa"", 0H~). 

Special kinds can be found in the table or often under the 
compound itself. It is well to remember that the ion 
corresponding to the common radical ammonium (NH4) 
is NHi-^. 

The numher of electric charges on an ion is equal to the 
valence of the corresponding atom or radical (221). Thus 
Na^ and Xa+, Ba" and Ba++, SO4" and SOr ", AP" and 
A1+++. Moreover, just as the total valences of the two 
parts of a compound are equal, so the total number of 
each kind of charges (+ and — ) is equal. For example, 
Na^CP and Xa+, Cb ; Alo"' "' (804)3" " " and 2AI+++, 
3804" ~. We may define the valence of an ion as the 
number of electric charges it carries. 

247. Degree of ionization of acids, bases, and salts. — 
Except in unusual cases solutions of acids, bases, and salts 
contain both molecules and ions. That is, not all the 
molecules dissociate into ions. The degree of dissociation 
depends upon the concentration of the solution and also 
upon the electrolyte itself. In concentrated solutions the 
number of molecules is large. As the solution is diluted, 
more and more molecules dissociate into ions. Thus, in 
sodium hydroxide solution containing about 40 gm. in a 
liter the per cent of the ionized base is 73, whereas it is 
90 in a solution containing 4 gm. in a liter. In contrast 



2l6 



PRACTICAL CHEMISTRY 



to this, the degree of dissociation of acetic acid solutions 
containing respectively 60 gm. and 6 gm. in a Uter is only 
0.4 and 1.3 per cent of ionized acid. This means that 
acetic acid is weak ; it contains a small per cent of ions. 
Whereas sodium hydroxide is strong ; it contains a large 
per cent of ions. In contrast, nitric acid is a strong acid 
and ammonium hydroxide is a weak base. 

Strong acids and bases are almost completely dissociated 
in dilute solutions, and weak ones are only shghtly disso- 
ciated. We do not call salts "weak" or ''strong," be- 
cause they dissociate to about the same degree (unless they 
undergo hydrolysis (452)). 

The approximate per cent of dissociation of certain acids, 
bases, and salts in solutions of the same relative concen- 
tration and at the same temperature is shown in the ac- 
companying Table of Per Cent of Ionization. 

Table of Per Cent of Ionization 



Substance 



Hydrochloric Acid . . 

Nitric Acid 

Sulphuric Acid 
Acetic Acid .... 
Potassium Hydroxide 
Sodium Hydroxide . 
Ammonium Hydroxide 
Potassium Chloride . 
Silver Nitrate . 
Barium Chloride . 



H+, Cl- 
H+, NC3- 
H+, HSO4" 
H+, C2H3O2- 
K+, OH- 
Na+, OH- 
NH4+, OH- 
K+, Cl- 
Ag+, NO3- 
Ba++, 2CI- 



Per Cent of 
Ionization 



90 
90 
60 

1-3 
90 
90 

1.4 

86 
86 

72 



EXERCISES 



1. Prepare a summary of this chapter. 

2. State the theory of ionization. Illustrate it. State briefly 
the facts that support the theory. 



IONS AND lONIZAl ION 217 

3. Define and illustrate ion, anion, cation, electrode, anode, cathode, 
positive electrode, negative electrode. 

4. Distinguish between an atom and an ion of potassium. How 
is each represented? 

6. Name the ions in a solution of (a) hydrochloric acid, (b) sodium 
chlorate, (c) calcium hydro.xide, (//) sodium nitrate, (c) zinc sulphate. 

6. Learn the chemical expression for these ionized elements or 
radicals: (a) Hydrogen, sodium, potassium, silver, ammonium; 
(b) chloride, nitrate, hydroxyl ; (c) calcium, barium, copper, zinc, magne- 
sium, lead, iron (ous) ; (d) sulphate, carbonate; (c) aluminium, iron (ic). 

7. Interpret neutralization by the theory of ionization. Write 
the fundamental equation for neutralization. 

8. Interpret by the theory of ionization ((7) test for a chloride; 
(b) test for a sulphate. 

9. Define acid, base, and salt in terms of the theory of ionization. 

10. Define electrolysis. Interpret electrolysis of (a) hydrochloric 
acid, (b) sodium h^'droxide, (r) copper sulphate by the theory of ion- 
ization. 

11. Write ionic equations for (a) potassium chloride and silver ni- 
trate form silver chloride and potassium sulphate, and (b) barium ni- 
trate and sodium sulphate form barium sulphate and sodium nitrate. 

12. Describe fully the electrolysis of sodium sulphate solution. 

13. What is the difTerence between strong and weak electrolytes? 

14. Topics for review and home study: (a) Electroplating. 
(6) Arrhenius. (c) Valence, (d) Faraday's work on electrolysis. 
(e) Prepare a list of the new chemical words in this chapter and define 
each. (/) Degree of ionization of acids, bases, and salts. 

PROBLEMS (REVIEW) 

1. If 36 gm. of -copper are heated in air until there is no farther in- 
crease in weight, what is the name, formula, and weight of the product ? 
Ans. 45.07 gm. 

2. Equal weights of sodium and calcium interact with water, ard 
the liberated gas is collected. Which metal yields the larger volume? 
Write the equation for each reaction. 

3. How many grams of zinc must be used with hydrochloric acid to 
produce 750 cc. of dry hydrogen at 20° C. and 765 mm.? Ans. 2.05 gm. 

4. At what temperature will i 1. of chlorine weigh the same as i 1. 
of hydrogen? (Assume constant pressure.) 

5. One gram of a metal liberated 1.242 1. of hydrogen from hydro- 
chloric acid. The specific heat of the metal was found to be about 0.2 ?. 
Calculate (a) the equivalent weight and (b) atomic weight of the metal. 
What is the name of the metal? What is its valence? 



CHAPTER XIX 

SULPHUR AND SULPHIDES 

248. Introduction. — Sulphur is a familiar and useful 
element. This element, its compounds, and the various 
chemicals derived from it play a fundamental, and often 
indispensable, part in many industries. It is an ingredient 
of gunpowder. Considerable is used in the manufacture 
of fireworks. Large quantities are consumed in the rubber 
industry, especially in making automobile tires. In the 
paper industry, sulphur is employed in making the sul- 
phite needed to convert the wood into pulp. Sulphur 
is a constituent of mixtures for killing insect pests. These 
mixtures, e.g. lime-sulphur spray, liberate sulphur upon 
the injurious insect. Sulphur itself is also used as an in- 
secticide, especially for killing Phylloxera — an insect which 
destroys grapevines. 

Large quantities of sulphur are used in making sulphur 
compounds, such as sulphur dioxide (SO2), sulphur mono- 
chloride (S2CI2), carbon disulphide (CS2), and especially 
sulphuric acid (II2SO4). 

249. Occurrence. — Large deposits of free sulphur occur 
in volcanic regions, such as Japan and Mexico. Other 
deposits, as in Sicily, were doubtless formed by the action 
of microorganisms on calcium sulphate. 

Sulphur compounds are abundant, e.g. lead sulphide 
(galena, PbS), zinc sulphide (sphalerite or zinc blende, ZnS), 
mercuric sulphide (cinnabar, HgS), copper sulphide (chal- 
cocite, CU2S, and chalcopyrite, CuFeS2), iron sulphide 

218 



SULPHUR AND SULPHIDES 



219 



(iron jn-ritcs, FcS-j), and calcium sulphate (gypsum. 
CaS04.2H20). 

Volcanic gases often contain sulphur dioxide (SO2). and 
hydrogen sulphide (H2S) is found in the water of sulchur 
springs. Sulphur is 
a constituent of cer- 
tain organic com- 
pounds present in 
onions, horseradish, 
mustard, and eggs. 
Some varieties of coal 
and petroleum con- 
tain sulphur com- 
pounds. 

250. The sulphur in- Fig 
dustry. — Until about 




Apparatus for purifying sulphur 
by distillation 



1903 Sicily furnished most of the sulphur. Enough sul- 
phur for domestic and foreign uses is now readily ob- 
tained from the large deposits in Louisiana and Texas. 

In Sicily the deposits are not deep. The sulphur deposit is dug 
and removed from the mine by hand labor. The mass, which con- 
tains a large per cent of rock and earth, is piled loosely in a heap and 
ignited at the bottom. Some of the sulphur burns and the heat 
melts the rest, which drains away from the impurities. 

The crude sulphur may be purified by distillation in an apparatus 
like that shown in Fig. 87. The melted sulphur flows from the res- 
ervoir B into the retort .1, where it is boiled. The vapors pass into 
the large brick chamber and condense upon the cold walls as a fine 
powder, called flowers of sulphur. As the operation continues, the 
walls become hot, and the sulphur collects on the floor as a liquid ; 
this is drawn off through the tap C into cylindrical wooden molds 
and allowed to cool. These sticks are called roll sulphur or brimstone. 

In the United States the sulphur deposits are from 500 
to 1000 feet deep. The sulphur is brought to the surface 



220 



PRACTICAL CHEMISTRY 



A—^ 




by an ingenious method devised by American chemists. 
A hole is drilled through the overlying soil, sand, and rock 
into the sulphur deposits below. The well, as it is called, 
is equipped with a set of pipes, one 
inside the other. The pipes, inclosed 
in a casing, are driven down through 
the hole (Fig. 88). The outermost 
pipe is the casing (not shown in the fig- 
ure). The remaining pipes are the 
essential ones ; let us call them A , B, 
and C. Through A water at 170° C. 
and under 100 pounds pressure is 
forced down to the bottom ; this very 
hot water flows out into a large area 
around the well and melts, the sul- 
phur, which collects in a pool at the 
"-^ bottom of the pipes. Through C (the 

^^' : ^^ , ^' ^ f "^ smallest pipe) hot air is forced down 

of pipes used in the ^ ^ ^ 

United States to melt and forms a froth with the sulphur, 
sulphur and bring it This froth. Owing to the pressure of the 

to the surface ^^^ ^^^^^ ^^^^ ^.^^ ^j^^^ through B 

(the middle of the three pipes) and flows out at the 
surface into a large wooden bin, where it cools and solidi- 
fies into huge blocks (Fig. 89). 

A single well often produces over 500 tons of sulphur a 
day. Some of the blocks contain as much as 100,000 
tons of sulphur. When the whole block is cold, the 
wooden sides of the bin are removed, the sulphur is 
blasted into fragments, and loaded into cars by steam shovels 
(Fig. 90). The American sulphur industry is conducted 
on a prodigious scale, and yields large quantities of sulphur, 
which is so pure (about 99.5 per cent) it can be used with- 
out further treatment. 



SULPHUR AND SULPHIDES 



221 



251. Properties of sulphur. — Sulphur is a pale yellow, 
brittle solid, which sometimes has a faint odor. It is in- 
soluble in water and most acids. Most varieties dissolve 




Fig. Sq. — Sulphur flowing from a well (left). Huge block of soliditied 
sulphur {right) 




Fig. 90. — Loading sulphur into cars by a steam shovel (left), partly- 
removed blocks of sulphur {center) derricks for drillin;^ machinery (right) 

readily in carbon disulphide and in sulphur chloride 
{i.e. sulphur " monochloride," S2CI2). Sulphur does not 



222 PRACTICAL CHEMISTRY 

conduct electricity at all well. Its conductivity is lower 
than that of practically any other soHd substance ; this 
fact is sometimes expressed by saying sulphur is a good 
insulator. Nor does it conduct heat well, its heat con- 
ductivity being but one half that of cork and one quarter 
that of ice. The specific gravity of the solid is about 2, 
i.e. it is about twice as heavy as water. 

When heated, sulphur melts at about 114° C. to a thin, 
pale yellow hquid. As the temperature rises, the hquid 
darkens and thickens ; at about 160° C. it is dark brown 
and viscous, at about 230° C. it is black and too thick to 
flow from the vessel, while at about 445° C. it becomes 
thin again, boils, and turns into yellow sulphur vapor. 

Sulphur molecules contain eight atoms (Sg) at low temperatures 
of the vapor, while at 800° C. the molecules contain two atoms (S2). 
At about 2000° C, sulphur is monatomic (S). 

252. Chemical conduct of sulphur. — Sulphur is an 
active element, especially when heated. It combines 
readily and directly with many elements. Thus, it ignites 
readily in the air and burns with a pale blue flame, forming 
sulphur dioxide gas (SO2) ; if burned in oxygen, a little 
sulphur trioxide (SO3) is also formed. Moist sulphur is 
oxidized, slowly, by the oxygen of the air. Thus : — 

28 + 3O2 + 2H2O = 2H2SO4 

It combines directly with most metals, forming sulphides ; 
the reaction is often accompanied with much heat and 
light, as in the case of zinc, copper, and iron (3). It also 
combines directly with carbon to form carbon disulphide 
(258), and with chlorine to form sulphur chloride (S2CI2). 
253. Different modifications of sulphur. — If sulphur 
is dissolved in carbon disulphide and the solution evaporated 
slowly, the sulphur is deposited as small crystals. Well- 



SULPHUR AND SULPHIDES 



223 





formed crystals have eight sides and belonp; to the ortho- 
rhombic system (Fig. 91). It is called orthorhombic. or 
sometimes rhombic, sulphur. Crystallized native sulphur 
is orthorhombic. Roll sulphur and flowers of sulphur 
also are orthorhombic, though the 
crystals are so interlaced or so small 
that their shape is obscured. 

Another variety, called monoclinic. 
is obtained by letting melted sulphur 
cool slowly. If sulphur is melted in Fig. 91. — Orthorhombic 
a crucible and the excess of hquid '^^y^^^ so su p ur 
poured off as soon as crystals shoot out from the walls 
near the surface, the interior of the crucible is found to 
be Hned with long, dark yellow, shin- 
ing needles (Fig. 92). They are mono- 
clinic crystals of sulphur. In a few 
days they turn dull and opaque, and in 
time change into small orthorhombic 
crystals. If monoclinic sulphur is kept 
above 96° C, it does not change. 

These two modifications of sulphur have 

different physical properties. Orthorhombic 

Fig. 92. — Section of sulphur has the specific gravity 2.07 and melts 

a crucible showing at 112.8° C. (if heated rapidly). The corre- 

monocUnic crystals sponding values of monoclinic sulphur are i.q6 

of sulphur ^^^ jj^ 25° C. 

If sulphur is boiled or heated above the viscous stage 
and then cooled quickly by pouring into water, a tough, 
rubberlike, amber-colored solid is formed. It is called 
amorphous or plastic sulphur. It is insoluble in carbon 
disulphide. Plastic sulphur when first formed is non- 
crystalline and for this reason is called amorphous (" with- 
out form "). It is unstable, and soon becomes hard, brittle, 




2 24 PRACTICAL CHEMISTRY 

and yellow ; after considerable time it changes in part into 
orthorhombic crystals. Its specific gravity is 1.89. 

The different modifications of sulphur are elementary sulphur, 
though they have different properties. Each burns to sulphur diox- 
ide, and the same weight of each yields the same weight of sulphur di- 
oxide {i.e. ^2 grams of each yields 64 grams of sulphur dioxide). An 
element which has different forms is called an allotropic element, and 
the different forms are called allotropic forms (278). 

254. Hydrogen sulphide (H2S) is the gaseous compound 
of sulphur and hydrogen with a notoriously bad smell. It 
occurs in the waters of some " sulphur springs " and in 
some volcanic gases. The air near sewers and cesspools 
often contains this gas, since it is one product of the decay 
of animal substances which contain sulphur. The albumin 
in the white part of eggs contains sulphur, and when eggs 
decay, hydrogen sulphide is formed ; hence the bad smell. 

255. Preparation of hydrogen sulphide. — The gas is usually 
prepared in the laboratory by the interaction of dilute hydrochloric 
or sulphuric acid and ferrous sulphide. The equation is : — 



FeS 


-f 2HCI 


HoS 


+ 


Fed. 


Iron 


Hydrochloric 


Hydrogen 




Iron 


Sulphide 


Acid 


Sulphide 




Chloride 



The apparatus shown in Fig. 13 may be used. All experiments in- 
volving hydrogen sulphide should be done in a hood. 

256. Properties of hydrogen sulphide. — Hydrogen sul- 
phide is a colorless gas. It has the odor of rotten eggs. 
It is poisonous. A httle, even if diluted with air, often 
produces headache and nausea, and a large quantity of the 
gas may prove fatal. One volume of water dissolves about 
three volumes of hydrogen sulphide gas at ordinary tem- 
peratures. The solution is often called hydrogen sulphide 
water, and can be used instead of the gas in many chemical 



SULPHUR AND SULPHIDES 225 

experiments; it has a weak arid reaction, and is sometimes 
called hydrosulphuric acid. In terms of the ionic theory 
the solution contains tew ions (H+ and S" "). Like all 
acids it forms salts; the salts are called sulphides (257). 

Hydrogen sulphide gas catches lire easily and burns with 
a bluish llame, forming sulphur dioxide and water thus : — 

2H,S + 3O2 = 2SO2 -f- 2H2O 

Hydrogen Sulphide Oxygen Sulphur Dioxide Water 

If the supply of air is insufficient, combustion is incomplete, 
and sulphur and water are formed, thus : — 

2H2S + O2 = 2S + 2H0O 

Hydrogen Sulphide Oxygen Sulphur Water 

Hydrogen sulphide reduces nitric acid and sulphuric acid ; 
the equation for the latter reaction is : — 

H2S + H2SO4 = SO2 + S -h 2H0O 

Hydrogen Sulphuric Sulphur Sulphur Water 

Sulphide Acid Dioxide 

257. Sulphides may be regarded as salts of the weak acid 
hydrogen sulphide, though they are not always prepared 
directly from hydrogen sulphide. They can be produced 
by the direct union of sulphur and metals, as in the case of 
iron sulphide previously mentioned (3), or by exposing 
metals to the moist gas. 

Sulphides are usually prepared in the la])oratory by pre- 
cipitation. That is, the gas is passed into solutions of 
certain salts, or hydrogen sulphide water is added. 

Many sulphides are black, one (zinc sulphide) is white, 
and several have a characteristic color. Thus, arsenic 
sulphide is pale yellow, manganese sulphide is tlesh colored, 
and antimony sulphide is orange red. The color often 
affords a ready means of identifying each sulphide. 



2 26 PRACTICAL CHEMISTRY 

Copper, tin, lead, and silver react readily with hydrogen 
sulphide and are rapidly tarnished by exposure to the gas. 
Silverware turns brown or black, especially in houses heated 
by coal and lighted by coal gas, probably owing to the small 
quantity of hydrogen sulphide from these sources. A 
brown film (silver sulphide) also coats silver spoons which 
are put into mustard, eggs, and some vegetables, such as 
cauliflower. Lead compounds are blackened by this gas, 
owing to the formation of lead sulphide, thus : — 



PbO 


+ 


H2S 


PbS 


+ 


H2O 


Lead 




Hydrogen 


Lead 




Water 


Oxide 




Sulphide 


Sulphide 







For this reason buildings painted with " white lead " paint 
often become dark, and, similarly, oil paintings are dis- 
colored. The blackening of paper moistened with a solu- 
tion of lead nitrate or acetate is the customary test for 
hydrogen sulphide. 

258. Carbon disulphide (CSo) when pure, is a clear, 
colorless, heavy liquid, with an agreeable odor, but the 
commercial substance is yellow and has an exceedingly 
offensive smell. It is poisonous. It vaporizes very readily 
and is highly inflammable. The equation for its com- 
bustion is : — 

CSo -f 3O2 = CO.2 + 2SO.2 

Carbon Disulphide Oxygen Carbon Dioxide Sulphur Dioxide 

Since its vapor burns readily and catches fire easily, the 
Uquid must be used with care. No flames should be near 
when carbon disulphide is being evaporated or used as a 
solvent. 

Carbon disulphide is practically insoluble in water. It 
is a useful solvent because it dissolves rubber, gums, fats, 



SULPHUR AND SULPHIDES 



227 




rGJ_ 







E 



iodine, camphor, and some forms of sulphur. It is a highly 

refracting liquid, and hollow glass prisms filled with it are 

used to decompose Ught. Considerable is used to kill 

insects on both living and dried 

plants {e.g. in museums), and to 

exterminate ants, mice, moles, and 

woodchucks. 

Carbon disulphide is manufactured 
from carbon and sulphur by an electro- 
thermal process. A diagram of the fur- 
nace is shown in Fig. 93. Several groups 
of carbon electrodes (EE) are set into 
the base of the furnace, coke is packed 
loosely between them, and the body of 
the furnace is filled with charcoal (C). 
Sulphur is introduced at suitable points 
(5, 5. 5), and coke is fed in through K, K. 
When the electric current passes, the heat 
caused by the resistance offered by the 
coke melts the sulphur (Z), which rises 
and unites with the heated carbon 
above the electrodes. The vapors of the carbon disulphide escape 
through a large pipe (P) and are condensed in a special apparatus. 

EXERCISES 

1. Where is free sulphur found? Xame five or more native com- 
pounds of sulphur. 

2. Give the name and formula of five metallic sulphides. 

3. Summarize (a) the physical properties, and (b) the chemical 
conduct of sulphur. 

4. State the uses of sulphur. 

5. ?Io\v is sulphur obtained from deposits in the United States? 
Draw (from memory) a diagram of the system of pipes. 

6. Given several yellow powders, how would you prove by experi- 
ment which one is sulphur? 

7. What is (a) roll sulphur, (/)) brimstone, (c) rhombic sulphur, 
(d) monoclinic sulphur, (e) amorphous sulphur, (/) monatomic sulphur? 

8. Compare rhombic and monoclinic sulphur. 



Fig. 93. — Electrothermal 
furnace for manufactur- 
ing carbon disulphide 



228 PRACTKWI. (^IIKMISIRV 

9. Ilow is hydrogen sulphulc prcpiireci? Slate the equation. 

10. Suniniiirize the properties of hydrogen sulphide. 

11. State i>ne or more tests ior h\'dro<xen suljihide. 

12. Write these eciuatioiis in the ordiiuuN' ami the ionic form: 

(a) Lead nitrate and hydrogen sulphide form lead sulphide and nitric 
acid. (/)) Copper sulphate and hydrogen suljdiide form ct)jiper sulphide 
and sulphuric acid. 

13. Describe the manufacture of carbon disuljihide. Draw (from 
memor\-) a diagram of tlu- furnace. 

14. Write the M^lumetric e(|uation for the lombustion of (j) h}'dro- 
gen sulphiile ^^wilh excess of air), antl (/») carbon disulphide. 

PROBLEMS 

1. What is the aii['»ro\imate weight of sulphur in a bin joo feet 
long, 8o feet wide, and go feet high? (Xdi'k. — .V cubic foot of water 
weighs a{)pro.\imately 6j pounds.) 

2. Calculate the weight of sulphur in [ii) 500 gm. of pure FeS., 

(b) a kilogram of CS^... 

3. Calculate the weight of sulphur in {^l) 77 gm. i^f pure 1I.;SD4, 
(/)) 77 1. of HjS at -^o" C. and 755 mm. 

4. Hydrochloric acid solution having the specit"ic gravity of 1.2 
contains ^^o.So per cent of HCl (by weight). What {a) weight ami 
(b) volume oi hydrogen sulj^hide (at standard contlitions) will be pro- 
duced b>' the interaction of iron sulj^hiile (l'"eS) and j 1. of this acid? 

5. If 100 cc. of hydrogen sulphide are burned in air. what volume 
of (<i) o.xygen is consumed and (/>) sulphur dioxide produced? 

6. Suppose a liter of carbon disulphide vapor burns in air. 
(rt) What voUune oi oxygen is consumed? (/') What is the volume of 
each product ? 

7. Write the fi>rmula of the sulphide oi hydrogen, sodium, silver, 
calcium, /.inc. lead, aluminium, potassium, copper, NH4, Sn (ous). 

8. Calculate the simplest fi^rmula corresponding to {ii) S = jg. 
As = (M ; (/') S = jo.o, .Vs = 70.1. 

9. Calculate the atiHiiic weight of sulphur from ((/) 10 gm. of silver 
yield 11.4S15 gm. of silver sulphide (assume -VgjS and .\g = 107. 88) ; 
(b) 2 gm. of lead yield .'. 0:184 gm. of lead sulphate (make the correct 
assumptions). 

10. Complete and balance (w) HoS -\ = CuS H ; {b) CdCla 

-h' = CdS ^ 



CHAPTER XX 

SULPHUR OXIDES, ACIDS, AND SALTS 

259. Introduction. ■ - Sulphur forms two oxides sul- 
phur dioxide (SO2) and sulphur trioxide (SO3). There 
are two acids corresponding to these oxides — sulphurous 
acid (H-iSCi) and sulphuric acid fH2S0}). Both acids 
form numerous salts. 

260. Formation and preparation of sulphur dioxide. — 
When sulphur burns in air (or oxygen), sulphur dioxide 
is formed, thus : — 

S + O2 = SO2 

Sulphur Oxygen Sulphur Dioxide 

Many sulphur compounds, when burned, yield sulphur 
dioxide. The gas is also formed when certain sulphur 
compounds, e.g. sulphuric acid, are decomposed. 

On an industrial scale, the gas is prepared by burning 
sulphur or by roasting metallic sulphides, especially iron 
disulphide (iron pyrites, FeS2) in air, thus : — 

4FeS2 + 11O2 = 8SO2 + 2Fe203 

Iron Disulphide Oxygen Sulphur Dioxide Iron Oxide 

Both of these reactions (sulphur and sulphide) are utilized 
on a large scale in the manufacture of suli)huric acid. 

In the laboratory two methods of preparation are used, 
(i) If copper and concentrated sulphuric acid are heated, 
a series of complex changes results finally in the evolution 
of sulphur dioxide. The equation may be written : — 

229 



230 PRACTICAL CHEMISTRY 



Cu + H.2SO4 


= SO2 + 


CUSO4 


Copper Sulphuric 


Sulphur 


Copper 


Acid 


Dioxide 


Sulphate 



+ HoO 



(2) More commonly dilute sulphuric (or hydrochloric) 
acid is dropped upon a sulphite. The equation is : — 

NasSOs + H2SO4 = SO2 -f Na2S04 + H2O 

Sodium Sulphuric Sulphur Sodium 

Sulphite Acid Dioxide Sulphate 

The sulphite method is safer and more convenient, es- 
pecially for liberating a steady current of the gas. Some- 
times the gas is obtained from a cylinder 
of liquid sulphur dioxide (Fig. 94). 

261. Properties of sulphur dioxide. — 
Sulphur dioxide is a colorless gas. Its 
odor is suffocating, being the well-known 
odor associated with burning sulphur. 
The gas is a little more than twice as heavy 
as air. A liter at 0° C. and 760 mm. 
weighs 2.9 gm. Sulphur dioxide is readily 
Hquefied ; the hquid is a common article of 
Fig. 94. — Cylin- Commerce and can be more conveniently 
der of liquid used than similar liquids {e.g. chlorine or 
sulphur dioxide ^^^^^^^y ^he gas is very soluble in 
water ; at ordinary temperatures one volume of water 
dissolves about forty volumes of gas. This solution is sour 
and reddens blue litmus ; besides sulphur dioxide it con- 
tains sulphurous acid (262). 

Sulphur dioxide does not burn and will not support 
ordinary combustion. 

262. Sulphurous acid (H2SO3) is prepared by dissolving 
sulphur dioxide in water. The gas combines with the 



SULPHUR 
DIOXIDE 



SULPHUR OXIDES, ACIDS, AND SALTS 231 

water to some extent. The simplest equation expressing 
this fact is : — ■ 

SOo + H2O = H2SO3 

Sulphur Dioxide Water Sulphurous Acid 

Sulphur dioxide is often called sulphurous anhydride, be- 
cause it is the anhydride of sulphurous acid. Anhydrides 
of non-metals are acid anhydrides, i.e. non-metaUic oxides 
which unite with water to form acids (266). 

Sulphurous acid is unstable and decomposes readily into 
sulphur dioxide and water, especially when the solution 
is heated ; solutions of sulphurous acid smell strongly of 
sulphur dioxide. The formation and decomposition may 
be represented as a reversible equation, thus : — 

SO2 + H20:;itH2S03 

Sulphurous acid is readily oxidized. Solutions of the 
acid, if exposed to air, soon give a test for sulphuric acid, 
which is formed by the combining of the sulphurous acid 
with oxygen from the air. Oxidizing agents, such as potas- 
sium permanganate, produce this change quickly. The 
oxidation of sulphurous acid to sulphuric acid is expressed 
by this equation : — 

2H2SO3 + O2 = 2H2SO4 

Sulphurous Acid Oxygen Sulphuric Acid 

We can also describe this chemical change by saying sul- 
phurous acid is a reducing agent. 

263. Salts of sulphurous acid. — Sulphurous acid forms 
two classes of salts — the normal and the acid sulphites. 
When the two atoms of hydrogen in sulphurous acid are 
replaced by a metal, the product is a normal sulphite. But 
if only one atom is replaced, the product is an acid sulphite. 



232 PRACTICAL CHEMISTRY 

Acids like sulphurous acid, which have two replaceable 
hydrogen atoms, are called dibasic acids. 

Normal sodium sulphite (Na2S03) is formed when sul- 
phurous acid is neutralized by sodium hydroxide, thus : — 

HoSOs + 2NaOH = NaoSOa + H2O 

Sulphurous Acid Sodium Hydroxide Sodium Sulphite Water 

Acid sodium sulphite (HXaSOs), often called bisulphite of 
soda, is formed when only half as much base is used, thus : — 

H2SO3 + NaOH = HNaSOs + HoO 

Acid Sodium Sulphite 

Both kinds of salts yield sulphur dioxide by interaction 
with an acid (260 (2)). The acid salt is sometimes used as 
the antichlor to remove the excess of chlorine from bleached 
cotton cloth (150). It is also used in tanning, and in 
making starch, sugar, and paper. 

Acid calcium sulphite (Ca(HS03)2) is extensively used 
in one process of making paper from wood. The chips of 
wood are " cooked " in large vessels with a solution of acid 
calcium sulphite which dissolves the hgnin and leaves cel- 
lulose (352, 354). 

264. Uses of sulphur dioxide and sulphurous acid. — 
Vast quantities of sulphur dioxide are 
used in manufacturing sulphuric acid 
(267) and acid calcium sulphite (263). 
Infected clothing and rooms are some- 
times fumigated with sulphur dioxide ; 
Pig^ 95. — Sulphur the gas for household use maybe obtained 
candle for local fu- by burning a '' sulphur candle" (Fig. 
migation ^^y Dried fruits, canned corn, cherries, 

and nuts are bleached by sulphur dioxide or sulphurous 
acid. The moist gas — really a weak sulphurous acid 




SULPHUR OXIDES, ACIDS, AND SALTS 23.3 

solution — - is used to l^leach silk, hair, straw, paper, wool, 
and other substances which would be injured by chlorine. 
The effect of the moist gas can be shown by putting a 
wet colored flower into a bottle in which sulphur is burn- 
ing ; the flower soon loses its color. In some cases the 
bleached article, e.g. a straw hat, partially regains its 
color or becomes yellow. The effect of sulphur dioxide on 
organic matter is seen in localities where considerable gas 
escapes, e.g. near smelters and chemical works ; trees, 
shrubs, and other kinds of vegetation are blighted or de- 
stroyed. 

265. Preparation of sulphur trioxide. — Sulphur tri- 
oxide (SO3) is produced to a slight extent when sulphur 
burns in air or in oxygen ; it causes the white fumes often 
seen during the combustion. The reaction between sul- 
phur dioxide and oxygen is very slow. It can be hastened 
by passing a mixture of sulphur dioxide and oxygen (or air) 
over hot platinum or asbestos coated with platinum. Other 
substances also hasten the chemical change. The plat- 
inum, as far as we know, does not participate in this re- 
action. It hastens a very slow chemical reaction. 

As we have seen (53), substances which hasten a chem- 
ical reaction but are unchanged at the end of the process 
are called catalyzers or catalytic agents. Such a chemical 
reaction is said to be due to catalysis or catalytic action. 

266. Properties of sulphur trioxide. — Above 15° C. sulphur tri- 
oxide is a liquid, which boils at 46° C. Below 15° C. it is a white 
solid. When exposed to moist air, it fumes strongly, owing to the 
formation of sulphuric acid ; and when dropped into water it dis- 
solves with a hissing sound and evolution of heat. The equation 
for the combination of sulphur trioxide and water is : — 

SO3 + H2O = H0SO4 

Sulphur trioxide is called sulphuric anhydride. (Compare 261.) 



234 PRACTICAL CHEMISTRY 

267. Manufacture of sulphuric acid. — Enormous quan- 
tities of sulphuric acid are manufactured by two processes, 
known as the lead chamber process and the contact process. 
In each process sulphur dioxide is oxidized to sulphur tri- 
oxide, which with water forms sulphuric acid. A general 
equation for the essential chemical change is : — 

2SO2 + O2 + 2H2O = 2H2SO4 

In the lead chamber process the oxidation is accompUshed 
by nitrogen oxides ; and in the contact process it is hastened 
by a catalyst. 

In the lead chamber process sulphur dioxide, air, steam, 
and nitrogen oxides are introduced into large lead chambers. 
These gases react and produce sulphuric acid, which col- 
lects on the floors of the lead chambers. 

The chemical changes involved in this process are com- 
plex and variable. The two main reactions may be rep- 
resented thus : — 

2SO2 + NO + NO2 + O2 + H2O = 2S02(OH)(ONO) 

Nitrosyl-sulphuric Acid 

2S02(OH)(ONO) -\- H2O = 2H2SO4 + NO + NO2 

According to some authorities, nitrogen trioxide (N2O3) is 
the active oxide. The interpretation is simpler, however, 
if we assume the presence of nitric oxide (NO) and nitrogen 
dioxide (NO2). 

The main changes are three : (i) The sulphur dioxide 
is oxidized to sulphur trioxide by nitrogen dioxide, thus : — 

SO2 + NO2 = SO3 + NO 

(2) The sulphur trioxide with water forms sulphuric acid, 
thus : — 

SO3 + H2O = H2SO4 



SULPHUR OXIDES, ACIDS, AND SALTS 235 



(3) The nitric oxide unites with oxygen (from air) and 
forms nitrogen dioxide, thus : — 

2NO + O2 = 2NO2 

Hence, nitric oxide acts as a carrier of oxygen, so to speak, 
from the air to the sulphur dioxide. Some authorities 
speak of the nitric oxide as a catalyst. 




3i JHi) ^We ffimnA 



Fig. 96. — Diagram of plant for chamber process of manufacturing 
sulphuric acid 

These equations show that the oxides of nitrogen play an important 
part in the manufacture of sulphuric acid. Theoretically only a 
small quantity of nitrogen oxides is needed to form an unlimited quan- 
tity of sulphuric acid. However, some escapes and must be replaced ; 
this is done by putting nitric acid into the top of the Glover tower or 
injecting it into the chambers. 

268. The construction and operation of a chamber acid plant. — 
The plant (Fig. q6) consists of two main parts : (</) the furnace for 
producing sulphur dioxide, and (h) the lead chambers together with 
the Glover and Gay-Lussac towers for changing the gaseous mixture 
into sulphuric acid. 

The manufacturing operation is somewhat as follows : (i) Sulphur 



236 PRACTICAL CHEMISTRY 

or iron disulphide (FeS2) is burned in a furnace (.1) with enough air 
to change the sulphur into sulphur dioxide and to furnish the proper 
amount of oxygen for later changes. In some works the furnace is 
provided with " niter pots " to produce nitric acid vapor {i.e. nitro- 
gen oxides). 

(2) The mixture of sulphur dioxide, nitrogen oxides, and air passes 
from the furnace into the bottom of the Glover tower (B) . This is a tall 
tower filled with stones or pieces of earthenware over which flow two 
streams of sulphuric acid, one dilute (C) and the other {D) containing 
nitrogen dioxide (obtained from the Gay-Lussac tower acid). These 
acids cool the ascending gases ; at the same time the dilute acid is 
deprived of water and the Gay-Lussac tower acid of its dissolved 
nitrogen dioxide. Hence concentrated acid flows out of the bottom 
of the Glover tower (B) into the " strong acid " blower (£) , from which 
it is forced to the top of the Gay-Lussac tower for use as explained 
below ; while from the top of the Glover tower sulphur dioxide, nitro- 
gen oxides, and air pass into the first lead chamber (F). Here steam 
and nitric acid' are introduced. The main chemical changes occur 
in this and the second chamber. 

These chambers are huge boxes often having a total capacity of 
150,000 cubic feet; the walls and floors are of sheet lead supported 
on a wooden framework, lead being a metal which is only slightly 
attacked by the chamber acid. 

The nitrogen (from the original air) and the unused gases pass 
on (from the last chamber) into the bottom of the Gay-Lussac 
tower (G). This tower is filled with coke or earthenware over which 
flows concentrated sulphuric acid (H) (obtained from the blower E 
connected with the Glover tower) , which absorbs the unused nitrogen 
dioxide. The " nitrose " acid flows from the bottom of the Gay-Lussac 
tower into a blower (/) , whence it is forced to the top of the Glover 
tower, where, as stated above, the nitrogen dioxide is liberated. 

(3) The acid produced in the chambers, which flows into /, con- 
tains from 60 to 70 per cent of the compound H0SO4. For some uses, 
e.g. the manufacture of fertilizers, this acid needs no further 
treatment. Much of the acid, however, is concentrated by evapora- 
tion. It is first heated in lead-lined pans until the concentration is 
about 77 per cent, and finally in platinum, cast iron, or fused quartz 
vessels until the acid contains about 94 per cent of H0SO4 and has a 
specific gravity of 1.84. 



SULPHUR OXIDES, ACIDS, AND SALTS 237 



269. Manufacture of sulphuric acid by the contact 
process. — In this process sulphur dioxide and air, well 
purilied and heated to about 400° C, are brought in contact 
with a catalyst, — platinum, or, in some plants, iron oxide 
(FeoOa). The sulphur dioxide is thereby quickly oxidized 
to sulphur trioxide, thus : — 

2SO.2 + O2 = 2SO3 

Sulphur Dioxide Oxygen Sulphur Trioxide 

The sulphur trioxide is conducted into sulphuric acid con- 
taining a little water, because it is not absorbed quickly 
enough by w^ater alone. The sulphur trioxide combines 
with the w^ater, thereby producing sulphuric acid, thus : — 

SO3 + H2O = H0SO4 

Sulphur Trioxide Water Sulphuric Acid 

270. The construction and operation of a contact acid plant. — 
A sketch of the apparatus is shown in Fig. 97. The blower .1 forces 



^K 





Fig. 97. — Sketch of the apparatus for making sulphuric acid by the 
contact process 

air into the burner 5, where the sulphur dioxide is formed by burning 
iron pyrites (FeS2) or sulphur. The gases pass into the dust cham- 
ber C, where they are freed from sulphur dust and other solid im- 
purities ; this is an important step, for dust reduces the transforming 
power of the catalytic agent. The gases, cooled by the pipe D, are 
further cleaned in the scrubbers, which contain coke wet with 
water (£) and with sulphuric acid (F). The next step is the removal 
of arsenic compounds in the purifier G. During the combustion of 



238 PRACTICAL CHEMISTRY 

iron pyrites, arsenic compounds are liberated; traces of such com- 
pounds " poison " the platinum used as a catalytic agent and stop 
the formation of sulphur trioxide. The purified gases (mainly sul- 
phur dioxide) then enter the mixer and heater H. Here a large ex- 
cess of air is introduced from the blower and the whole mixture is 
heated to 400° C. This temperature is carefully regulated because 
at 400° C. the yield of sulphur trioxide is maximum (98-99 per cent). 

The purified and heated mixture of sulphur dioxide and air 
passes into the contact chamber /. Here the gases come in contact 
with the catalyst and form sulphur trioxide. The catalyst, if plati- 
num, consists of asbestos fibers coated with a very thin layer of metal- 
He platinum and is spread out on plates or mixed with porous material 
in order to provide a large contact surface. 

The final step is the transformation of the sulphur trioxide into 
sulphuric acid by combining with water; the trioxide is passed 
into the absorber (not shown). This is a large earthenware jug 
partly filled with sulphuric acid containing 2 to 3 per cent of water. 
In this Hquid, all the sulphur trioxide combines with water ; the 
supply of water is replenished to maintain the required concen- 
tration in the absorber. 

271. Properties of sulphuric acid. — Sulphuric acid is 
an oily hquid, colorless when pure, but often brown from 
the presence of charred organic matter, such as dust and 
straw. The specific gravity of the commercial acid is about 
1.84; thus it is nearly twice as heavy as water. It boils 
at about 338° C, decomposing to some extent and forming 
dense, white, suffocating fumes. 

When sulphuric acid is mixed with water, much heat 
is evolved. The acid should always he poured into the water 
and the mixture should he stirred, otherwise the intense heat 
may crack the vessel or spatter the hot acid. This tend- 
ency to absorb water is shown in many ways. The con- 
centrated acid absorbs moisture from the air and from 
gases passed through it. It is often used in the labora- 
tory to dry gases. Organic substances^ such as wood. 



SULPHUR OXIDES, ACIDS, AND SALTS 239 



paper, sugar, starch, and cotton, are charred by sulphuric 
acid (Fig. q8). Such compounds contain hydrogen and 
oxygen in the proportion to form water ; these two elements 
are abstracted and carbon alone remains. Sulphuric acid 
also disintegrates the flesh, often causing 
serious burns, and if accidentally spilled 
on the hands or spattered on the face 
should be washed off immediately. 

The interaction of sulphuric acid and 
metals varies. With many metals, di- 
lute sulphuric acid forms hydrogen and 
the corresponding metallic sulphate. 
Thus, hydrogen is usually prepared in 
the laboratory from zinc and sulphuric 
acid. Concentrated acid, especially if hot, converts most 
metals into an oxide, which is then transformed into the 
corresponding sulphate. Thus, the equations expressing 
the reactions with copper are : — 




Fig. 98. — Paper 
charred by sul- 
phuric acid 



Cu 

Copper 

CuO + 

Copper Oxide 



+ H.2SO4 = CuO + SO2 4- HoO 

Sulphuric Acid Copper Oxide Sulphur Dioxide Water 



H.2SO4 = CUSO4 + H2O 

Sulphuric Acid Copper Sulphate Water 



Iron is the only common metal that is not readily attacked 
by the concentrated acid, and advantage is taken of this 
property in transporting acid in bulk in iron tank cars. 

Sulphuric acid unites with ammonia (NH3) to form am- 
monium sulphate ((NRi)2S04). Hot concentrated acid 
oxidizes sulphur and carbon to sulphur dioxide and carbon 
dioxide. Thus : — 

2H0SO4 + C = COo + 2H0O -f 2SC2 

Owing to its high boiling point, sulphuric acid by inter- 



240 PRACTICAL CHEMISTRY 

action with the proper salt liberates acids having a low 
boiling point, e.g. hydrochloric and nitric acids (153, 183). 
Dilute solutions of sulphuric acid contain an abundance 
of hydrogen ions (H+) and sulphate ions (S04~~). The 
HSO4 ion is in solutions of certain concentration (247). 

272. Uses of sulphuric acid. — Sulphuric acid is one of 
the most important substances. Directly or indirectly 
it is used in hundreds of industries upon which the com-* 
fort, prosperity, and progress of mankind depend. It is 
used in the manufacture of many acids. It is essential 
in one process for the manufacture of sodium bicarbonate, 
which has many uses. The petroleum industry requires 
large amounts. Enormous quantities are consumed in mak- 
ing fertilizers, alum, and other sulphates, nitroglycerin, 
glucose, dyes, and in various parts of such fundamental 
industries as dyeing, bleaching, metal cleaning, refining, 
and metallurgy. 

273. Sulphates. — Sulphuric acid is dibasic and forms 
two classes of salts — the normal sulphates, such as sodium 
sulphate (Na2S04), and the acid sulphates (or bisulphates), 
such as acid sodium sulphate (HNaS04). 

Most sulphates are soluble in water ; only the sulphates 
of barium, strontium, and lead are insoluble, while calcium 
sulphate is but slightly soluble. Important sulphates 
are calcium sulphate (gypsum, CaS04.2H20), barium sul- 
phate (barite, barytes, heavy spar, BaS04), zinc sulphate 
(ZnS04, and white vitriol, ZnS04.7H20), copper sulphate 
(CUSO4, and blue vitriol or blue stone, CUSO4.5H2O), 
iron sulphate (FeSOi, and green vitriol, copperas, or ferrous 
sulphate, FeS04.7H20), sodium sulphate (Na2S04, and 
Glauber's salt, Na2S04.ioH20), and magnesium sulphate 
(MgS04, and Epsom salts, MgS04.7H20). Sulphates are 
used in many industries. 



SULPHUR OXIDES, ACIDS, AND SALTS 241 

274. The test for sulphuric acid or a soluble sulphate 
is the foniiation of white, insoluble barium sulphate upon 
the addition of barium chloride solution. Thus : — 

H2SO4 + BaClo = BaS04 + 2HCI 

Since sulphuric acid and solutions of sulphates contain 
SO4 ions and barium chloride (or nitrate) contains Ba ions, 
the ionic equation for the reaction is : — 

Ba++ + SO4- - = BaS04 

An insoluble sulphate fused on charcoal is reduced to a 
sulphide, which blackens a moist silver coin, owing to the 
formation of silver sulphide (Ag2S) ; this is the usual test. 

275. Fuming sulphuric acid (H2S2O7), is made by mixing sulphur 
trioxidc with sulphuric acid. This is the acid called sulphuric acid 
by the alchemists, who made it by heating moist ferrous sulphate. 
It is sometimes called Nordhausen sulphuric acid. It is a thick, 
brown liquid, which fumes strongly in the air, owing to the escape of 
sulphur trioxide. It is used in gas analysis to absorb ethylene and 
other illuminants, and in dyeing to dissolve indigo. If the fuming 
acid is cooled to 0° C, crystals separate; they are called pyro- 
sulphuric acid. Its salts are called pyrosulphates. 

276. Sodium thiosulphate (NasSoOa) is a salt of an unstable acid. 
It is sometimes incorrectly called sodium hyposulphite, or simply 
*' hypo." It is a white, crystalHne solid, very soluble in water. The 
solution, used in excess, dissolves certain compounds of silver, 
i.e. AgCl, AgBr, Agl ; hence its extensive use in photography (589). 



EXERCISES 

1. Describe the lead chamber process of making sulphuric acid. 

2. Starting with sulphur, how would you prepare successively 
sulphur dioxide, sulphur trioxide, sulphuric acid, hydrogen sulphide, 
and sulphur? 

3. Describe the contact process of manufacturing sulphuric acid. 

4. Enumerate the important uses of sulphuric acid. 



242 PRACTICAL CHEMISTRY 

5. What is (a) gypsum, (b) white vitriol, (c) green vitriol, (d) blue 
vitriol, (e) Glauber's salt, (/) oil of vitriol, (g) " hypo," {h) calcium 
bisulphite ? 

6. State the test for (c) sulphuric acid, (b) sulphurous acid, (c) a 
soluble sulphate, (d) an insoluble sulphate, (e) a sulphite, (/) H2S. 

7. Essay topics: (a) Uses of sulphuric acid, (b) Normal and acid 
sulphates, (c) Bleaching with sulphur dioxide. 

8. Show how the two oxides of sulphur illustrate the law of 
multiple proportions. 

9. Explain the following : (a) Bottles of concentrated sulphuric acid 
sometimes have a white deposit inside the bottle and a black one 
outside, (b) Dishes of concentrated sulphuric acid are often left inside 
of a chemical balance. 

10. Write the formula of (a) the sulphite, (b) the acid sulphite, (c) 
the sulphate, (d) the acid sulphate of K, NH4, Ca, Pb, Ag, Ba, Zn, 

PROBLEMS 

1. Write the equation for the interaction of sodium sulphite and 
sulphuric acid. W^hat weight and what volume (standard conditions) 
of sulphur dioxide can be prepared from 25 gm. of sodium sulphite 
(92 per cent pure)? 

2. In Problem 1 what volume of sulphuric acid solution is needed, 
if the acid used has the specific gravity 1.45 and contains 55.07 per cent 
of H0SO4 by weight? 

3. How much sulphur (99 per cent pure) is needed to manufacture 
100 tons of sulphuric acid containing 5 per cent of water? 

4. An oxide of sulphur contains 50 per cent of each element. If 
the atomic weights of oxygen and sulphur are respectively 16 and 32, 
what is the molecular formula of the compound? 

5. A flask filled with water was found to weigh 72 gm., the flask 
alone weighing 22 gm. The flask filled with sulphuric acid weighed 
114 gm. Calculate the specific gravity of the sulphuric acid. 

6. Suppose a manufacturer of H2SO4 starts with 100 tons of sulphur 
and obtains the theoretical yield in each case : (a) What weight of 
oxygen is needed to burn the sulphur to sulphur dioxide ? (b) What 
additional weight of oxygen to convert the sulphur dioxide to sulphur tri- 
oxide? (c) What weight of water to convert the sulphur trioxide to 
sulphuric acid? (d) And how much sulphuric acid is obtained? 

7. What weight of pure H2SO4 can be manufactured from 150 tons 
(2000 lb. each) of iron pj-rites containing 92 per cent of FeSo? 

8. What weight of sulphuric acid having a specific gravity of 1.84 
is contained in a cylindrical tank 20 m. long and 1.3 m. in diameter? 



SULPHUR OXIDES, ACIDS, AND SALTS 243 

9. What weight and what volume of sulphur dioxide fat standard 
conditions) will sulphuric acid and 57 gm. of copper produce? 

10. Calculate the weight of sulphur in (a) 2000 lb. of sulphuric acid 
solution (93.19 per cent pure), and (b) 2 kg. of nitrosylsulphuric acid. 

11. What weight of pure sulphuric acid can be made from 1000 tons 
of pure sulphur? From 1000 tons of pure FeS2? 

12. Calculate the atomic weight of sulphur from the following 
analyses of sulphur compounds : (a) S = 40 per cent, molecular weight 

= 80; (b) S = 23.529, m. w. = 136; (c) S = 20.125, m. w. = 159. 

13. Calculate the simplest formulas corresponding to (a) S = 36.36, 
Fe = 63.63; (b) S = 53-33, Fe = 46.66; (c) S = 32.65, O = 65.31, 
H = 2.04; (d) S = 39-02, O = 58-53, H = 2.44. 

14. How many liters of oxygen are needed (a) to form 10 liters of 
sulphur dioxide (from sulphur), and (b) to transform 10 liters of sul- 
phur dioxide to sulphur trioxide ? 



CHAPTER XXI 
CARBON (Continued) — CARBONIC ACID — CARBONATES 

277. Introduction. — In Chapter III we found that 
carbon is a useful and an important element. We 
studied, also, carbon dioxide (CO2) and carbon mon- 
oxide (CO). So important are carbon and these two com- 
pounds it would be well to read Chapter III carefully be- 
fore continuing the study of this fundamental element. 

In this chapter we shall study carbon more in detail, 
its only acid (carbonic acid), the carbonates, and one car- 
bide (calcium carbide, CaC2). In the three succeeding 
chapters we shall study fuels and flames, other carbon com- 
pounds, and food. 

278. Carbon is an allotropic element. — Carbon exists in different 
modifications. The two crystalline varieties are diamond and 
graphite. Amorphous carbon includes many kinds of familiar sub- 
stances, e.g. charcoal, coal, lampblack, and coke. Although the 
crystalline and amorphous varieties have quite different properties, 
they are elementary carbon. They can be changed into one another. 
Indeed, graphite is manufactured from coal (280). Diamonds, too, 
have been made from charcoal. Each modification burns in oxygen 
and yields only carbon dioxide. Furthermore, a given weight of each 
yields the same weight of carbon dioxide. Carbon, like sulphur, is an 
allotropic element (253). 

279. Diamond is pure crystalline carbon. As found 
in nature, diamonds are rough-looking stones, which must 
be ground, or " cut," into special shapes and poKshed to 
bring out the luster and make them sparkle in the light 

(Fig. 99)- 

244 



CARBONIC ACID — CARBONATES 



245 



Diamond has the high specific gravity of 3.5, 
of the hardest substances known, and can be ' 



It is one 
cut '' and 




Crystal Rough 

Fig. 99. — Diamonds 



Cut 



polished only by other diamonds (with sharp edges) or 
by diamond powder. 

Diamonds that are badly flawed or are black are used to cut glass 
and as the cutting part of the diamond drill. The inner surface of 
the entering end of the drill is set with black diamonds. The drill 
in passing through rocks and hard deposits cuts a solid core, which is 
brought to the surface for examination. 

Diamond resists the action of most chemicals, though 
it combines with oxygen when the two elements are heated 
together to a high temperature. Diamond is carbon, for 
when pure diamond is burned in oxygen, the only product 
is carbon dioxide. Diamonds have been made from carbon. 
The French chemist Moissan in 1893 dissolved pure char- 
coal in melted iron, and suddenly cooled the molten mass 
in water. The pressure caused the cooHng carbon to 
crystallize into very small crystals of diamond. 

The largest diamond thus far found was called the Cullinan. It 
was found in 1905 in South Africa, where many diamonds are mined. 
It weighed about 3025 carats (1.37 lb. avoir. ).^ Stones cut from it 
are among the crown jewels of England. 

280. Graphite is another variety of crystalline carbon. 

It is a soft, friable, dark lead-colored, shiny solid, which 

^ The international carat, which is the unit of weight used in weighing and 
selling diamonds, is equal to 200 milligrams. 



246 PRACTICAL CHEMISTRY 

is smooth and greasy to the touch. Pure graphite is car- 
bon ; but it is sometimes called " black lead," or plumbago, 
because it was formerly supposed to contain lead. Unlike 
diamond, graphite is a good conductor of electricity and 
is often used to coat molds in electro typing (243). It is 
so soft that it readily wears away ; hence it blackens the 
fingers and leaves a black mark on paper when drawn across 
it. This property is indicated by the name graphite, which 
is derived from a Greek word meaning to write. It resem- 
bles diamond in its insolubility in liquids at the ordinary 
temperature. Its specific gravity is 2.2, being consider- 
ably lighter than diamond. 

Graphite changes into carbon dioxide when heated in- 
tensely in oxygen ; but it can be heated to a very high tem- 
perature in the air without melting or undergoing ap- 
preciable change. 

Graphite is used to make stove poHsh and protective 
paints. As a solid lubricant it is used where oil might 
be decomposed by heat or might clog machinery. It is 
the principal ingredient of the mixture (graphite and clay) 
which is made into graphite crucibles ; these crucibles can 
be heated to a high temperature, and certain metals, e.g. 
steel, are made in them. Some varieties of artificial 
graphite can be ground into very fine particles. If ground 
with tannin (or a similar substance), and mixed with oil 
or water, this graphite is converted into the colloidal state 
(86). Such mixtures of graphite make excellent lubricants. 

In making lead pencils, the graphite is washed free from impurities, 
ground to a fine powder, mixed with more or less clay, and then pressed 
through perforated plates, from which the " lead " issues in tiny rods. 
These are dried, cut into the proper lengths, baked to remove all 
traces of moisture, and then inserted in the wooden case. Soft pencils 
contain more graphite and less clay than hard ones. 



CARBONIC ACID — CARBONATES 



247 



Graphite occurs abundantly, the famous locaHties being 
Ceylon and Siberia. Considerable graphite is also manu- 
factured at Niagara Falls by heating a special grade of hard 
coal out of contact with air in an electric furnace. The 




Fig. 100. — An electric furnace for making gra[)hite 

process is electrothermal, i.e. the chemical change is brought 
about by the intense heat produced by passing an electric 
current through the materials (Fig. 100). Articles of al- 
most any size can now be made of artificial graphite, which 
is so compact that it can be further shaped by tools. This 
kind of graphite is especially suitable for the electrodes 
used in electrolytic and electrothermal apparatus. 

281. Amorphous carbon includes all varieties of coal 
and charcoal, lampblack, coke, and gas carbon. They are 
the non-crystalline forms of impure carbon. The word 
amorphous (253) means without crystalline form ; it is 
often used to designate soft, powdery, and uncrystallized 
substances. 

282. There are many varieties of coal. — It is customary 
to speak of two principal kinds of coal, though several vari- 



248 



PRACTICAL CHEMISTRY 



eties of each are common articles of commerce, (i) Bi- 
tuminous coal (soft coal) contains about 70 per cent of 
carbon. It burns with a smoky flame, and is used to make 
illuminating gas, coke, and as a fuel for steam. (2) An- 
thracite coal (hard coal) contains 90 per cent or more of 
carbon. It ignites with difflculty, burns with little or no 
flame, and produces considerable heat. It is used mainly 
for domestic purposes — heating and cooking — especially 
in eastern United States. Some varieties of coal, such 
as lignite or brown coal, contain only a small proportion 
of carbon, as low as 20 per cent. Yet they are used as 
fuel in some locahties. 

Besides carbon, coal contains moisture, ash or mineral 
matter; and soft coal, especially, contains considerable 
volatile matter, which consists mainly of compounds of 
carbon with hydrogen, nitrogen, and sulphur. 

283. How coal was formed. — Ages ago the vegetation was ex- 
ceedingly dense and luxuriant upon the land slightly raised above the 




Fig. loi. — Section of the earth's crust showing layers of coal 



sea. In process of time this vegetation decayed, accumulated, and 
slowly became covered with sand, mud, and water. This vegetable 
matter was then slowly changed into more or less impure carbon, mois- 
ture, and gaseous and liquid compounds called hydrocarbons. The 
geological and chemical changes were repeated, and as a result we 
find in the earth layers or seams of carbonaceous matter varying in 
thickness and composition (Fig. loi). These are the coal beds. Coal 
beds contain proofs of their vegetable origin, viz. impressions of vines, 
stems, and leaves of plants, and similar vegetable substances. 



CARBONIC ACID — CARBONATES 



249 



(Fig. 102). A thin section of coal examined through a microscope 
reveals a distinct vegetable structure (Fig. 103). 

284. Charcoal is obtained by heating wood, bones, and 
other organic matter in closed vessels, or by partially 





Fig. 102. — Fossil found in a Fig. 103. — Section of coal as seen 
coal bed through a microscope 

burning them in the air. Besides carbon, charcoal con- 
tains mineral matter. 

285. Wood charcoal is a black, brittle solid, and often 
retains the form of the wood from which it is made. It 
is insoluble, though its mineral impurities can be removed 
by acids. It burns without flame or much smoke, and 
leaves a white ash which consists of mineral substances. 
The compact varieties conduct heat and electricity, but 
porous charcoal is a poor conductor. It resists the action 
of moisture and many chemicals ; hence fence posts, tele- 
graph poles, and wooden piles are often charred before 
being put into the ground. 

Most varieties are very porous, and are excellent ab- 
sorbers of gases. Sewers, cisterns, and foul places are 
sometimes purified by charcoal. It will also absorb colored 
substances from solutions. Foul air and water may be 



250 PRACTICAL CHEMISTRY 

partially purified by charcoal, which forms the essential 
part of many water filters in houses and air filters in large 
buildings. Charcoal used for such a purpose, however, 
must be frequently renewed or often heated to redness ; 
otherwise it becomes clogged and contaminated. Large 
quantities of charcoal are used as a fuel and in the manu- 
facture of steel and of gunpowder. 

Wood charcoal is made either in charcoal pits or in large iron fur- 
naces. Where wood is plentiful, it is loosely piled into a conical shape, 
and covered with turf. The wood is lighted, and as it slowly burns 
care is taken to regulate the supply of air so that the wood will 
smolder but not be entirely consumed. The volatile matter escapes 
and charcoal remains. 

Much charcoal is made by heating wood in closed furnaces, no air 
whatever being admitted. By this method, which is called dry 
distillation, the yield of charcoal is about 30 per cent. From the 
volatile matter we obtain acetic acid and methanol (or " wood 

alcohol"). 

More or less charcoal may be obtained by heating a compound 
of carbon, e.g. sugar or starch, the charring being a test for carbon. 

286. Animal charcoal or boneblack is made by heating 
bones and animal refuse in a closed vessel. The animal 
charcoal from bones contains only about 10 per cent of 
carbon, but this carbon is distributed throughout the porous 
mineral matter of the bone (largely calcium phosphate). 
Animal charcoal is used as a pigment, especially in making 
shoe-blacking. It is also extensively used to remove the 
color from sugar sirups. 

287. Coke is made by expelling the volatile matter from 
bituminous coal, somewhat as charcoal is made from wood. 
It is Jef t in the retorts when coal is distilled in the manu- 
facture of coal gas (326). On a large scale it is made by 
heating a special grade of soft coal in huge brick ovens 
from which air is excluded after combustion begins. Owing 



CARBONIC ACID — CARBONATES 251 

to the loss of valuable by-products, the older kinds of ovens 
are being replaced by closed furnaces, called by-product 
ovens (Fig. 104), constructed so as to save the by-products, 




Fig. 104. — A battery of by-product coke ovens at one of the Ford auto- 
mobile plants 

e.g. ammonia, tar, organic compounds, and combustible 
gases. 

Coke is a grayish, porous soHd, harder and heavier than 
charcoal. It burns with no smoke and a feeble flame. Its 
most extensive use is in the iron industry (489). 

288. Gas carbon is a variety of amorphous carbon which is de- 
posited on the inside of the retorts used in the manufacture of illumin- 
ating gas (326). It is a black, heavy, hard solid, and is almost pure 
carbon. It is a good conductor of electricity, and is extensively 
used for the manufacture of the carbon rods of electric lights and for 
plates of electric batteries. 

289. Lampblack is prepared by burning gas, oil, or oily substances 
rich in carbon in a limited supply of air. The dense smoke, which is 
finely divided carbon, is passed through a series of condensing cham- 
bers, where it is collected upon coarse cloth or a cold surface. 



252 



PRACTICAL CHEMISTRY 



Lampblack is one of the purest forms of amorphous carbon, and it is 
used in making printer's ink and certain black paints. 

290. Chemical conduct of carbon. — Carbon does not 
interact with acids or bases. At ordinary temperatures 
carbon is inactive, but it is active at high temperatures. 
Thus, carbon heated with oxygen forms carbon dioxide and 
carbon monoxide, and with sulphur, carbon disulphide 
(258) . Carbon unites with many metals and some non-met- 
als in the electric furnace, thereby forming carbides, e.g. 
calcium carbide (CaC2) and carborundum (siHcon carbide, 
CSi) (295, 392). At high temperatures carbon is a reduc- 
ing agent ; extensive application of this 
property is made in producing metals 
from ores, e.g. iron from iron oxide (489). 

A simple experiment can be made to illus- 
trate the reducing action of carbon. A mixture 
of powdered charcoal and copper oxide is put 
in a test tube fitted with a one-hole stopper and 
a delivery tube bent at a right angle. The test 
tube is clamped to an iron stand so that the 
end of the delivery tube dips into a bottle half 
full of limewater (Fig. 105). When the mix- 
ture is heated, carbon dioxide is evolved and 
produces a white precipitate (CaCOs) in 

the limewater. Metallic copper (not easily seen) is left in the 

test tube. The equation is : — 

C + 2CuO = CO2 -h 2Cu 

291. Carbon dioxide — review and extension. — Carbon 
dioxide is one product of ordinary combustion, respiration 
of animals, fermentation, and decay. The equation for 
the combustion of carbon in air or oxygen is : — 

C + O2 = CO2 

Carbon Oxygen Carbon Dioxide 

The fact that carbon dioxide is formed by the free com- 




Fig. 105. — Reducing 
copper oxide with 
carbon 



CARBONIC ACID — CARBONATES 253 

bustion of carbon and carbon compounds may be shown 
by bubbling the smoke from these burning substances 
through calcium hydroxide solution. 

The continuous oxidation of the tissues of the body also 
produces carbon dioxide (27). If we exhale the breath 
through a glass tube into calcium hydroxide solution 
(Fig. 12), the carbon dioxide that is in the breath turns 
the solution milky — the usual test for carbon dioxide. 

Many kinds of organic matter ferment, especially those 
containing certain varieties of sugar. By alcoholic fer- 
mentation the sugar changes into carbon dioxide and alco- 
hol, thus : — 

C6H12O6 = 2CO.2 + 2C2H5OH 

Sugar Carbon Dioxide Alcohol 

Carbon dioxide is usually prepared by the interaction 
of a carbonate and an acid. Calcium carbonate (limestone 
or marble) and hydrochloric acid are ordinarily used, 
thus : — 

CaCOs + 2HCI = CO. + CaClo + HoO 

Calcium Hydrochloric Carbon Calcium Water 

Carbonate Acid Dioxide Chloride 

Carbon dioxide has a slight taste but no color. It is 
heavier than air (1.5 to i), and a liter under standard con- 
ditions weighs 1.98 gm. This gas dissolves readily in water 
— especially under pressure — a property utilized in manu- 
facturing beverages (Figs. 14, 15). 

Carbon dioxide docs not burn nor support combustion. 
This property is utilized in fire extinguishers. It combines 
to some extent with water, forming carbonic acid (292). 

The gas is not poisonous, but its presence in the air of 
a room to any extent is objectionable. Carbon dioxide 
bears an impressive relation to the life of plants and animals. 



254 



PRACTICAL CHEMISTRY 



Plants absorb it and transform it into starch, while animals 
eat and assimilate starch, and exhale carbon dioxide into 

the atmosphere ready 
for the plants again (39). 
This relation, which is 
often called the cycle of 
carbon and oxygen, is 
shown by a diagram in 
Fig. 17. 

One of the first to study 
carbon dioxide was the Scotch 
chemist Black (Fig. 106). He 
not only observed and recorded 
its properties but also showed 
the relation of the gas to car- 
bonates. 

292. Carbonic acid. — 

Carbon dioxide is often 
ac [1/2 -1/99) called carbonic acid gas, 

or simply carbonic acid. These terms are incorrect when 
applied to carbon dioxide, and should be used only as 
the name of the compound H2CO3. If carbon dioxide is 
passed into water, it combines to some extent with the 
water and forms a weak, unstable acid, which is carbonic 
acid (H2CO3). The equation for this change is : - 

CO2 + H2O = H2CO3 

Carbon Dioxide Water Carbonic Acid 

Such a solution reddens blue litmus and decolorizes pink 
phenolphthalein solution, though its action is feeble. Car- 
bonic acid in terms of the theory of ionization is a weak 
acid, i.e. it ionizes only slightly, its ions being H+ and HCOa" 
(247). Carbonic acid is so unstable that it easily breaks 
up by gentle heat into carbon dioxide and water, thus : — 




Tls- 106 



CARBONIC ACID — CARBONATES 255 

H2CO3 = CO2 + HoO 

For this reason it cannot be obtained free like other acids. 

Carbon dioxide is sometimes called carbonic anhydride to em- 
phasize the fact that, like oxides of other non-metals, it unites with 
water to form an acid (262, 266). 

293. Carbonates are salts of carbonic acid. They are 
common substances, but unlike the acid, are stable under 
ordinary conditions. The most abundant natural carbon- 
ates are those of calcium, magnesium, and iron. Immense 
quantities of sodium carbonate are manufactured. 

Carbonic acid is dibasic, and forms two classes of salts, 
the normal and the acid (263, 273). Thus, normal 
sodium carbonate is XaoCOs, and acid sodium carbonate 
is XaHCOs ; the latter is often called sodium bicarbonate. 
Similarly normal calcium carbonate is CaCOa, and acid 
calcium carbonate is CaH2(C03)2 (or Ca(HC03)2). 

The relation between normal and acid calcium carbonate is in- 
teresting. The normal salt is almost insoluble in water ; the acid 
salt is soluble in water and is easily decomposed by heat into the 
normal salt. Acid calcium carbonate is readily formed from the 
normal carbonate by an excess of carbon dioxide. Thus, when car- 
bon dioxide is passed into water containing insoluble normal calcium 
carbonate in suspension soluble acid calcium carbonate is formed : — 

H0CO3 + CaCOa = CaH,(C03)o 

Carbonic Acid Calcium Carbonate Acid Calcium Carbonate 

CaH2(CO,)o = CaC03 + CO, -f HoO 

Acid Calcium Carbonate Calcium Carbonate Carbon Dioxide Water 

An example of this reaction is seen in caves. Since many under- 
ground waters contain carbon dioxide, these waters dissolve the lime- 
stone (CaCOg) over which they pass. When the dissolved acid cal- 
cium carbonate is decomposed (by heat or in some other way), the 
calcium carbonate is reprecipitated in the form of stalactites and sta- 
lagmites which adorn the interior of the caves (Fig. 162). 



256 PRACTIC\L CHEMISTRY 

294. Carbon monoxide — review and extension. — Car- 
bon monoxide is formed when carbon is burned in a limited 
supply of air, thus : — 

2C + O2 = 2CO 

Carbon Oxygen Carbon Monoxide 

It is also formed when carbon dioxide is reduced with carbon, 
thus : — • 

COo + C = 2CO 

When carbon monoxide burns in air (43) or in oxygen, 
carbon dioxide is formed, thus : — 

2CO + 0-2 = 2CO2 

The oxides are, therefore, closely related, passing readily 
into each other (44). 

Carbon monoxide is usually prepared by decomposing oxalic acid 
with hot sulphuric acid, thus : — 

C2H,04 = CO + CO2 + H2O 

Oxalic Acid Carbon Monoxide Carbon Dioxide 

The carbon dioxide may be removed by passing the gases through 
a solution of sodium hydroxide. 

Carbon monoxide has no color, odor, or taste, and is 
only shghtly soluble in water. 

Carbon monoxide is poisonous. Air containing one part 
of carbon monoxide in 2000 produces unconsciousness, 
and ultimately causes death. Care should be taken to 
prevent its escape into rooms occupied by human beings 
(42) or into an unventilated garage. 

Carbon monoxide burns in air with a bluish flame (44). 
At a high temperature carbon monoxide readily reduces 
oxides, and is an important agent in the reduction of iron 
ores in the blast furnace, thus : ' — 



CARBONIC ACID — CARBONATES 



257 



Feo03 

Iron Oxide 



+ 3C0 = 

Carbon Monoxide 



2Fe + 3CO2 

Iron Carbon Dioxide 

Carbon monoxide forms no acid and no salts. It does not turn 
calcium hydroxide milky, thus being readily distinguished from car- 
bon dioxide. Its blue flame serves as a test to distinguish it from 
many other combustible gases. 

295. Calcium carbide (CaC2) is a brittle, dark gray, 
crystalline solid. It is made from coke or coal and lime 
(calcium oxide, CaO) in an electric furnace. The chemical 
change is caused solely by the intense heat and may be 
represented thus : — 

CaO 



3C 



+ 



CaG 



-f 



CO 



Carbon 



Calcium Oxide Calcium Carbide Carbon Monoxide 







A sketch of the furnace in which calcium carbide is made is shown 
in Fig. 107. The mixture of coke and lime (shown in the furnace) is 
introduced through the 
trap cover A and slowly 
sinks down into the 
space where the intense 
heat is produced by the 
electricity as it passes 
between the electrodes 
G and E, E. The liquid 
calcium carbide is drawn 
off through F. The 
carbon monoxide rises 
through the pipes D, D 
and enters the upper 
part of the furnace, to- 
gether with air supplied 
through C, C ; this mix- 
ture burns and heats 
the coke and lime. The waste gases (carbon dioxide and nitro- 
gen) escape through B. 




107 



P-lectric furnace for makinj 
calcium carbide 



The most striking and useful property o* calcium car- 



258 PRACTICAL CHEMISTRY 

bide is its action with water, acetylene being formed, 
thus : — 

CaCo + H2O = C2H2 + Ca(0H)2 

Calcium Carbide Water Acetylene Calcium Hydroxide 

Calcium carbide is used to generate acetylene, which is 
an illuminant (333). 

EXERCISES 

1. Prepare a summary of (a) the element carbon, (b) carbon diox- 
ide, (c) carbon monoxide. 

2. State the uses of (a) diamond, (b) graphite, (c) coke, (d) char- 
coal. 

3. Prepare a summary of the chemical conduct of carbon. 

4. Give a brief account of the manufacture of lead pencils. What 
is the literal meaning of the word graphite ? 

5. Describe the process of manufacturing graphite. 

6. Does carbon in the amorphous varieties differ chemically from 
pure diamond and graphite? Why? 

7. Prepare a summary of coal. 

8. The specific gravity of charcoal is about 1.5. Why does it 
float on water? 

9. Topics for home study: (a) Famous diamonds, (b) Carbon 
in electrical industries, (c) Carbon in paints, (d) The cycle of 
carbon in nature, (e) History of carbon dioxide. (/) Fire extin- 
guishers, (g) Carbon is an allotropic element. 

10. What is the relation of carbon dioxide to (a) respiration, (6) fer- 
mentation of sugar, (c) decay, (d) making lime, (e) combustion? 

11. Carbon and carbon monoxide are reducing agents. Explain 
and illustrate by equations. 

12. In what ways can carbon dioxide be prepared ? Give equations 
for the reactions. 

13. State fully the relation of carbon dioxide to carbonic acid. Give 
the equations for the formation and decomposition of this acid. 

14. What are carbonates? Acid carbonates? Illustrate by formulas. 
16. Illustrate Gay-Lussac's law by the carbon oxides. 

16. Write the formulas of the normal and acid carbonates of Ca, 
Ba, copper, Pb, potassium, silver, zinc. 

PROBLEMS 

1. Calculate the per cent of carbon in (a) carbonic anhydride, 
(6) acid calcium carbonate, (c) carbon monoxide, (d) marble. 



CARBONIC ACID — CARBONATES 259 

2. What weight of carbon is contained in 2 I. of carbon monoxide? 
In 2 1. of carbon dioxide? (Standard conditions.) 

3. What volume at standard conditions is occupied by (a) 70 gm. 
of carbon dioxide, and by ih) 45 gm. of carbon monoxide? 

4. Calculate the molecular weight of carbon dioxide if 10 1. weighs 
19.8 gm. 

6. How much oxygen by weight and by volume (standard con- 
ditions) is needed to convert the following into carbon dioxide : 
(a) I kg. of pure charcoal, {h) a diamond weighing 250 milligrams, and 
(c) 30 gm. of graphite? 

6. Show that the two carbon oxides illustrate the law of multiple 
proportions. 

7. Thirt}' grams of carbon are burned to carbon dioxide. What 
weight of potassium chlorate will provide the oxygen ? 

8. Calculate the simplest formulas from the following data : 
(a) 3 liters of a carbon oxide weigh 3.75 gm ; {h) C = 27.27, O = 
72.72 ; (r) an oxide of carbon contains 42.857 per cent of carbon. 

9. Carbon dioxide is heated with 40 gm. of carbon. What is 
(a) the weight and (&) the volume of the product? 

10. If 75 gm. of carbon dioxide are passed over hot carbon, what 
(a) weight of carbon is used and {h) volume of new gas is produced? 

11. What weight of carbon (97 per cent pure) is needed to reduce 
60 gm. of carbon dioxide to carbon monoxide ? What volume of air 
(containing 21 per cent of oxygen by volume) at 19° C. and 758 mm. is 
needed to change the carbon monoxide to carbon dioxide? 

12. How many cubic decimeters of carbon monoxide wall be formed 
by the decomposition of 25 gm. of oxalic acid? 

13. If one volume of carbon monoxide and two volumes of oxygen 
are mixed and exploded in a closed space, what will be the volume of 
the resulting gas or gases at the original temperature and pressure? 

14. A ton of calcium carbide is needed. What weight of lime (CaO) 
and coke (95 per cent pure) must be used? 



CHAPTER XXII 
FUELS — ILLUMINATING GASES — FLAME 

296. Carbon as a source of heat and light. — Carbon 
and many of its compounds burn readily in air and liberate 
considerable heat. Some compounds give also a colored 
flame, usually yellow. Carbon and certain carbon com- 
pounds are used as a source of heat and light, i.e. as fuels 
and illuminants, in our homes and in the industries. 

297. Fuels. — Solid fuels include wood, charcoal, coke, 
and the various kinds of coal (282). The commonest liquid 
fuels are fuel oil and gasolene, though kerosene and alcohol 
are used to some extent. The important gaseous fuels are 
natural gas and producer gas, though coal gas, water gas, 
and acetylene are also used to some extent. 

298. Illuminants are gases or readily volatihzed hquids. 
Illuminating gas made from coal or oil is the best known 
gaseous illuminant (327, 329, 330). Acetylene (CoHo) is 
another gas used as an illuminant (333). Kerosene is the 
commonest liquid illuminant. 

299. Composition of fuels. — Charcoal and coke are 
nearly pure carbon. Hard coal is about 90 per cent carbon, 
and soft coal about 70 per cent. All kinds of coal contain 
mineral matter, which is left as ashes when the coal is 
burned. Soft coal also contains considerable moisture 
and volatile matter. Wood is composed mainly of cel- 
lulose — a compound of carbon, hydrogen, and oxygen ; 
water (10 to 50 per cent) and mineral matter are also 
present. 

260 



FUELS — ILLUMINATING GASES — FLAME 261 

Liquid fuels (except alcohol) are mixtures of hydrocar- 
bons, i.e. compounds of carbon and hydrogen. Alcohol 
is a compound of carbon, hydrogen, and oxygen (C2H5OH). 

Gaseous fuels contain hydrocarbons (317), hydrogen, 
and carbon monoxide. 

300. Combustion of fuels. — When heated to the proper 
temperature fuels burn. Chemically this means that the 
carbon, hydrogen, and carbon monoxide unite with oxygen 
furnished by air. The gaseous products of combustion 
are carbon dioxide, carbon monoxide, and water. The 
solid products are the ashes and, if combustion is incom- 
plete, smoke. Heat is liberated when fuels burn. In- 
deed, the essential characteristic of a good fuel is its heat- 
producing capacity, especially when used to produce steam. 

301. Measurement of heat produced by fuels. — Heat, 
like other forms of energy, is measured by a special unit. 
The unit used in measuring the heat produced by fuels 
is called the British thermal unit (B.t.u.). It is the amount 
of heat that will raise the temperature of one pound of 
water 1° F. Thus, coke and very good soft coal will each 
produce about 16,000 B.t.u. per pound. Fuel oil, now 
used on warships and steamships, yields about 19,800 
B.t.u. per pound. Fuel gases (producer, water, and coal 
gas) give 145 to 600 B.t.u. per cubic foot. 

Another heat unit is called the small calorie (cal.). It is the 
amount of heat required to raise the temperature of one gram of 
water 1° C. (usually 15° to 16°). It is convenient to know that 
I B.t.u. = 252 cal. On the calorie basis, the heat value of good 
soft coal is about 8700 calories per gram. 

The large calorie (Cal.), which is one thousand times the small 
calorie, is used when the heat value is large. The heat value, often 
called the fuel value, of different kinds of food is usually expressed 
in large calories, e.g. one gram of starch in burning gives out 4 Cal- 



262 PRACTICAL CHEMISTRY 

ories and one gram of fat 9 Calories. (See also Fuel Value, 
Chapter XXIV.) 

302. The calorimeter is used to find heat value. — The 

heat, or fuel, value of such soUds as coal, charcoal, and 
food (dried) is measured by burning the solid in a bomb 
calorimeter. The essential part of the apparatus is a strong 
metal vessel, called a bomb, which is immersed in another 
vessel containing a known weight of water. 

In making a determination, a weighed amount of the substance 
is put in the bomb, a looped wire is dipped into the substance and the 
ends of the wire are connected with the electrodes on the bomb, the 
cover is screwed on, and oxygen is forced into the bomb (to hasten 
the combustion). The bomb is next placed inside the vessel con- 
taining a known weight of water. This outer vessel is well insulated 
so that all the heat produced in the bomb will be absorbed by the 
water. The vessel is also provided with an accurate thermometer 
and a stirrer. The substance is ignited by passing an electric current 
through the looped wire. The heat from the burning substance 
raises the temperature of the water, and the rise is carefully noted. 
From the weight of the substance, the weight of the water, and the 
rise in temperature (together with certain allowances for the appara- 
tus itself), the heat value of the substance can be computed. 

303. Thermo-chemical equations. — The heat liberated when 
carbon, or a carbon compound, burns can be incorporated in the equa- 
tion expressing the chemical change. Thus, the equation for the 
burning of charcoal in oxygen is : — 

C + O2 = CO2 + 97,000 cal. 

In this equation C stands for 12 grams of carbon, O2 for 32 of oxygen, 
and CO2 for 44 of carbon dioxide. Similarly : — 

2H2 + 02= 2H2O + 116,200 cal. 

Here 2H2 means 4 grams of hydrogen, O2 32 grams of oxygen, and 
2H0O 36 grams of water. Such equations are called thermo-chemical 
equations. 

304. Burning of coal. — When coal is burned, the prod- 
ucts of combustion depend on the kind of coal and on 



FUELS — ILLUMINATING GASES — FLAME 263 

the proportion of air supplied. With an excess of air, hard 
coal and good soft coal produce carbon dioxide, water, 
and sulphur dioxide. If the air is insufficient, carbon mon- 
oxide and hydrogen sulphide are also formed, while some 
unburned carbon escapes as smoke. This Hmited com- 
bustion involves loss of heat. If too much air is supplied, 
heat is also lost '' up the chimney." 

The air needed for burning coal in stoves or under boilers 
is drawn in through an opening under the grate by the 
draft created by the natural tendency of the hot gases to 
rise up the chimney. To obtain the best results, the air 
supply should be about twice that required to change all 
the carbon to carbon dioxide and the hydrogen to water. 

305. Smoke consists largely of unburned carbon in the 
form of small particles called cinders or soot ; some small 
particles of ash are often present. In large industrial plants 
where soft coal is used, improper burning adds to the smoke 
nuisance and also causes an enormous loss of heat. Some 
large factories have automatic smoke consumers as a part 
of the boiler equipment. By this device fuel is saved and 
smoke is prevented. Practically complete combustion is 
accompUshed by adding the fuel properly, regulating the 
supply of air, and using a special form of furnace. 

306. Burning hard coal in a stove. — For domestic pur- 
poses, hard coal is usually used. In 44 we learned that 
both carbon dioxide and carbon monoxide are formed in a 
coal fire in a stove. We can now interpret this fact. (See 
Fig. 108.) When air enters the bottom of the grate and 
comes in contact with the burning coal, oxygen unites with 
carbon to form carbon dioxide. The carbon dioxide rises 
through the hot coal, and the carbon reduces the carbon 
dioxide to carbon monoxide. Some of the carbon monoxide 
usually escapes, but most of it burns with a flickering 



264 



PRACTICAL CHEMISTRY 




bluish flame on the top of the fire, forming carbon dioxide 
with the oxygen of the air. 



2CO + 02= 2CO2 

CO2 + C = 2CO 

C +02= CO2 



Fig. loS. — The three main changes during combustion in a coal fire 

The combustion of coal in a stove or furnace in a house 
is regulated by dampers, usually three — one in the door 
below the grate (A), one in the door above the fire {B), and 
the third in pipe connected with the chimney (C) (Fig. 108). 
When the fire is built or needs to be '' started up," the 
dampers m the lower door and the pipe are opened but 
the one in the upper door is closed. This allows plenty of 
air to pass up through the burning coal and increase the 
combustion, and also creates a draft by permitting the 
hot products of combustion to rise and escape out of the 
chimney. Once started, the combustion in the fire can 
be regulated by closing the lower damper and opening the 
middle one, partly or wholly, and adjusting the chimney 
damper ; by this arrangement most of the air goes over the 
fire instead of up through it. 

Care must be taken to admit enough air through the lower door 
to burn the coal as completel}^ as possible so the maximum quantity 
of heat will be liberated. Incomplete combustion is expensive. 
Special care should also be taken to prevent the escape of " coal 
gas " into the house. This gas contains carbon monoxide, which is 
very poisonous (294), and hydrogen sulphide, which tarnishes silver- 
ware (256). 

307. Combustion of fuels is hastened by increasing 



FUELS — ILLUMINATING GASES — FLAME 265 

the rate at which air is suppHed. Before stoves were in 
common use, a bellows was used to ^' make the fire burn 
better." A blacksmith uses a bellows to make his lire 
hotter. In the laboratory we often use a foot bellows (or 
air blast) to force air into a blast-lamp and burn the illu- 
minating gas completely (Fig. 29). On coal-burning steam- 
ships high speed is attained (especially on trial runs or 
emergency trips) by using a forced draft. That is, rapid 
combustion — and hence more heat — is caused by blowing 
air through the fire. Similar effects are produced in other 
ways. For example, increased draft is produced in a loco- 
motive by forcing steam through the smokestack, in a 
large manufacturing plant by using a very high chimney, 
or an airblast {e.(^. in making iron and steel), and in stoves 
and furnaces by closing the middle damper tight, opening 
the top damper, and leaving the lower door wide open. 

308. Burning other solid carbon fuels. — Charcoal is readily 
ignited, burns with a slight flame, and yields no smoke. Its heat 
value is 12,000 to 14,000 B.t.u. per pound. Coke also burns with a 
small flame and without smoke. Its heat value is about 14,500 B.t.u. 
per pound. Both charcoal and coke find extensive use in the iron 
and steel industry (489, 496). 

309. Burning wood. — Wood has been used as a fuel for ages. 
The hard varieties such as oak, ash, and maple are the best fuels. 
Dry wood yields from 5600 to 8000 B.t.u. per pound. A cord of 
seasoned hard wood has about the same heat value as a ton of bi- 
tuminous coal. 

The essential ingredient of wood is cellulose — a compound of 
unknown composition, though often expressed by the formula 
(C6Hio05)n. A provisional equation for its combustion is : — 

CeHioOs -h 60, = 6C0> H- 5H0O 

310. Liquid fuels. — Three products from petroleum — 
fuel oil, gasolene, and kerosene — are used as fuels. They 
are mixtures of hydrocarbons (317). In burning, these 




266 PRACTICAL CHEMISTRY 

compounds are decomposed ; the carbon forms carbon 
dioxide and the hydrogen forms water. 

311. Fuel oil must be supplied to the furnace in the form 
of spray. This is produced by forcing the oil through a 
fine opening or by blowing it with steam or air through an 
atomizer. 

The general principle on which the latter type of burner operates 
is shown in Fig. 109. Oil enters at A and flows through D into the 

mixing and atomizing chamber 

C. Steam enters at B and 

'^\C passes through F and E into the 

chamber C, where it cuts across 

the oil at an angle. Here the oil 

and steam mix and the pressure 

'b - ^^^^xmrnmrm^Mmm ^^^^^^ ^he oil as a fine spray out 

Fig. 109. - Fuel oil burner into the furnace, where it burns 

instantly. 
When the spray of oil burns, a large amount of heat is 
liberated, as high as 19.800 B.t.u. per pound in the case of 
some grades of fuel oil. 

Fuel oil is extensively used on warships and steamships, and in 
many manufactories. By using oil in place of coal to generate steam, 
additional space is provided for cargo, more efficient combustion is 
attained, speed may be greatly increased, and the cruising radius 
enlarged, to say nothing of the labor saved and cleanliness secured. 

312. Gasolene is the fuel used in the engines of auto- 
mobiles, trucks, motor boats, motor cycles, and airplanes. 
Gasolene is very volatile and the vapor burns readily. If 
the vapor is mixed with air and the mixture is ignited by 
an electric spark, the combustion is so rapid that it is prac- 
tically an explosion; the gases, suddenly expanded, exert 
pressure, which is converted by the machinery into steady 
and continuous motion. 

313. Kerosene is used as a fuel to a Hmited extent in engines and 



FUELS — ILLUMINATING GASES — FLAME 267 



cooking stoves. In some portable stoves kerosene is burned by means 
of a large wick (as in a lamp). 

314. Alcohol. — Different kinds of alcohol are used as fuel, usually 
on a small scale. They burn without smoke and have a high heat 
value. Methyl alcohol (CH3OH), also called wood alcohol (285) and 
methanol, boils at about 66° C. and burns with a pale blue flame. It 
gives about 9600 B.t.u. per pound. Ethyl alcohol (C2H5OH), also 
called grain alcohol or simply alcohol, is a colorless, volatile liquid, 
which boils at about 78° C. and burns with a nearly colorless flame ; 
the heat produced is about 12,700 B.t.u. per pound. 

315. The petroleum industry. — Petroleum is obtained 
from the earth in many parts of the world. In the United 
States the chief locah- 
ties are Oklahoma, Kan- 
sas, Ohio, Pennsylvania, 
Texas, Louisiana, and 
Cahfornia. Mexico and 
Russia are large produc- 
ers. Some is found in 
Roumania, GaHcia, and 
Japan. 

Crude petroleum is an 
oily hquid with an un- 
pleasant odor. Its color 
varies from straw to 
black ; it is greenish in 
reflected Hght. Most 
kinds float on water. 
Its composition is com- 
plex, but all varieties are essentially mixtures of liquid 
and solid hydrocarbons (317). Certain grades contain 
compounds of nitrogen and of sulphur. 

In some localities the oil issues from the earth, but it is usually 
necessary to erect a derrick, drill a deep hole, and insert a pipe into 















-^^Q 


A SH[_ 


-^^Y 




i 






^^K 


Uf, 


i 








m 


;<.>^"r^J'--'. _ 





Fit:, no. 



Derricks and pumps in an 
oil region 



268 PRACTICAL CHEMISTRY 

the porous rock containing the oil (Fig. no). Sometimes the oil 
" spouts " out of the well when first drilled, but after a time a pump 
is needed to draw it to the surface. 

The oil is forced by powerful pumps through large pipes 
to central points for storage, or more often many miles to 
the refinery, where the petroleum in separated into various 
commercial products by refining. The petroleum is first 
cleaned by settling and filtration. Then it is distilled by 
heating it in huge retorts (Fig. iii, bottom), condensing 
the vapors in coiled pipes immersed in cold water, and 
collecting the distillates in separate tanks. This process 
is called fractional distillation, since the petroleum is sepa- 
rated into parts or fractions. Certain products, e.g. fuel 
oil, are obtained from the residue left in the stills. 

The different distillates are further separated and purified by 
redistillation (Fig. in, top). The chief commercial products 
obtained are petroleum ether (boiling point 4o°-7o° C), gasolene 
(70°-! 20°), benzine (i2o°-iso°), kerosene (i5o°-30o°) ; there are 
various commercial grades of these products, which are distinguished 
by the range of boiling points or by the specific gravity. These 
liquids are mixtures of several different hydrocarbons (317). They 
are variously used as solvents, fuels, and illuminants. 

The unusual demand for gasolene has led to a modifi- 
cation of refining in order to increase the supply. The 
higher boiling oils are vaporized and the vapor is heated 
to a high temperature (35o°-45o° C.) and under increased 
pressure (4 to 5 atmospheres). By this treatment, which 
is called cracking, complex hydrocarbons decompose and 
form hydrocarbons within the gasolene range (317). 

Owing to its extensive use as an illuminant, kerosene is care- 
fully freed from readily inflammable liquids and gases, w^hich might 
cause an explosion, and from tarry matter and semi-solid hydrocar- 
bons, which would clog a lamp wick. This is done by agitating 
it successively with sulphuric acid, sodium hydroxide, and water 



FUELS — ILLUMINATING GASES — FLAME 269 








WBifm 


f 


Im^*^^' ^M^m 




Fig. III. — Refining petroleum. Fire stills (bottom), steam stills 
(top), agitators (middle) 



270 



PRACTICAL CHEMISTRY 



(Fig. Ill, middle). Commercial kerosene must have a legal flashing 
point. This is " the temperature at which the oil gives off sufficient 
vapor to form a momentary flash when a small flame is brought near 
its surface." The legal minimum flashing point in most states is about 
110° Fahrenheit (about 44 C). 

The oil left in the fire still (Fig. iii, bottom) after the 
removal of the low-boiHng liquids including gasolene, and 




Fig. 112. — Sketch of a plant for the separation of gasolene and fuel oil 
from petroleum 



sometimes kerosene, is the commercial fuel oil (316) . Other 
oil residues, and crude petroleum to some extent, are used 
as fuels. Specifications prescribe the properties of fuel 
oil, especially its heat value, freedom from water and sul- 
phur (compounds), and mobility. 

From the residue after the distillation of the kerosene many grades 
of lubricating oil are obtained ; also vaseline and paraflfin wax. Petro- 
leum oils yielding these products are said to have a paraffin base ; 
Pennsylvania and Ohio oils are examples. Mineral lubricating oils 
have largely replaced animal and vegetable oils. Vaseline finds 
extensive use as an ointment. Paraffin wax is made into candles and 
into a waterproof coating for many substances. The final residue 



FUELS — ILLUMINATING GASES — FLAME 271 



in the still is mainly carbon and is called petroleum coke ; it is made 
into electric light carbons. 

Some oils, such as those from Mexico and California, leave a thick, 
black pitch. These oils are said to have an asphalt base. 

316. Fuel oil and gasolene. — The steps in the separation 
of gasolene and fuel oil from petroleum are shown in 
Fig. 112. This figure also illustrates the general process 
of refining. The crude oil is pumped from the storage 
tank A into the still B (Fig. iii, bottom), which is 
heated on the bottom by a flame. The vapors pass into 
the condenser C, and the distillate flows into the receiving 
house D, where it is examined through look boxes (Fig. 113). 
The different portions 
(called fractions) are 
directed into the proper 
tank. After certain 
low-boihng hydrocar- 
bons (making up gaso- 
lene and kerosene chiefly) 
have been boiled off in 
the fire still, the residue 
is drawn off and stored 
in the fuel oil tank E. 
The benzine fraction F 
is pumped to the agita- 
tor G (Fig. Ill, middle) 
and then to the storage 
tank H. From here the 




Fig. 113. — Look buxL- in which the 
distillates can be examined as they 
flow from the condensers through 
the receiving house on to the special 
storage tanks 



liquid goes to the still /, which is heated by steam (Fig. 
Ill, top). The vapors are condensed in 7, the distillate 
received in A', examined, and directed into the proper 
tank — the main one being the gasolene tank L. 

317. Hydrocarbons are compounds of carbon and hydro- 



272 PRACTICAL CHEMISTRY 

gen. They number over two hundred. Many of them 
occur in petroleum, natural gas, asphalt, and coal tar. 
Hydrocarbons are divided into series according to their 
composition. The commonest series is the methane or 
paraffin series. The first members in order are methane 
(CH4), ethane (G2H6), propane (CsHg), butane (C4H10), 
pentane (C5H12), and hexane (CeHu). 

Other members have a numerical name, similar to pentane and 
hexane, which indicates the number of carbon atoms in the molecule. 
The first four members are gases. Under ordinary conditions the 
next ten members are Hquids, and the rest are solids. 

Petroleum is a mixture of many hydrocarbons, and most 
American varieties contain paraffin hydrocarbons. Gasolene 
is mainly a mixture of hexane (CeHu), heptane (C7H16), 
and octane (CsHis). Kerosene consists of hydrocarbons 
which are composed of ten to sixteen carbon atoms, vaseline 
twenty- two and twenty- three, and paraffin wax still higher. 

318. Other series of hydrocarbons are also named from the first 
member, e.g. ethylene, acetylene, benzene, and naphthalene. Ethylene 
(C2H4) is a colorless gas, which burns with a yellow flame. It is the 
chief illuminating ingredient of coal gas (329). Acetylene (C2H0) 
is fully described in 333. Benzene (CeH'e) is a colorless liquid and 
naphthalene (CioHg) is a white, lustrous crystalline solid. They burn 
with a yellow flame, and, like ethylene, contribute to the luminosity 
of coal gas (339). 

319. Methane occurs in coal mine gases, natural gas 
(320) , and marsh gas (the mixture formed in marshy places 
by the decay of vegetable matter under water). It burns 
with a pale, hot flame, and is an essential heat-producing 
constituent of illuminating gas (329) and natural gas. A 
mixture of methane and air explodes violently when ignited 
by a spark or flame. Terrible disasters sometimes occur 
in bituminous coal mines from this cause. When methane 



FUELS — ILLUMINATING GASES — FLAME 273 



burns or explodes, carbon dioxide and water are formed, 
thus : — 

CH4 -f 2O2 = CO2 + 2H2O 

Methane Oxygen Carbon Dioxide Water 

The carbon dioxide, called choke damp or black damp by 
the miners, often suffocates those who escape from the 
explosion (29 and Fig. 11). 

The miner's safety lamp was invented in 181 5 by Davy to prevent 
explosions. It is essentially an oil lamp surrounded by a cylinder of 
fine wire gauze instead of the usual chimney (Fig. 114). When taken 
into a mine where there are explosive gases, 
e.g. methane, the gas enters the lamp and 
burns inside, but the flame within does not ig- 
nite the gases outside because the wire gauze 
keeps them cooled below their kindling tem- 
perature. When miners notice changes in the 
lamp flame, they usually seek a safe place. 
IVIodified forms of the Davy lamp are used at 
the present time. 

The principle of the Davy lamp is illustrated 
in Fig. 115. A wire gauze is held above a Bun- 
sen burner, the gas is turned on, and lighted 
above the gauze. The flame will not pass Fig. 114. —A form 
through the gauze unless the latter becomes hot. of Davy's safety 

lamp (gauze cut 
320. Gaseous ^^^'^y to show in- 

fuels include nat- 
ural gas and the various mixtures 
obtained from coal, e.g. producer gas, 
water gas, and coal gas. Natural 
gas exists in the earth in Pennsyl- 
vania, Ohio, West Virginia, and other 
Fig. 115. - Experiment ^^^^^ ^f ^he United States, usually 

illustrating the princi- . . , ^ ■ r ^ 

pie of Davy's safety ^^ ^^§1^^^ where petroleum IS found. 
lamp It is obtained by boring wells. It 





D 



2 74 



PRACTICAL CHEMISTRY 



is about 90 per cent methane (CH4), which is the chief 
heat-producing constituent. The gas burns with a hot 
flame. The heat value is about 1000 B.t.u. per cubic foot. 
It is used as fuel to heat houses and to generate steam in 
many industries, e.g. making steel, glass, brick, and pottery. 
As a fuel it is cheap and efficient. A large volume of 
air and a special burner are needed for its combustion. 

321. Producer gas is made by forcing air (sometimes 
together with a little steam) through a deep coal fire in a 
special kind of furnace. The gaseous product contains 




(o^==a 



Fig. 116. — Diagram of water gas plant 

25 to 30 per cent of carbon monoxide, 50 to 60 per cent of 
nitrogen, and 10 to 13 per cent of hydrogen (if steam is 
used). Its heat value is rather low, about 145 B.t.u. 
per cubic foot, though it varies with the process, being 
higher if steam is used. This value is low on account of 
the large proportion of nitrogen. But the cost is not great, 
because the gas can be quickly made and efficiently 
burned. Producer gas is used as a fuel in gas engines and 
in many industrial and metallurgical operations. 

322. Water gas is made by forcing steam through a 
mass of hot coke or anthracite coal. It is essentially a 
mixture of hydrogen and carbon monoxide, and is used to 



FUELS — ILLUMINATING GASES — FLAME 275 

some extent as fuel. More often it is enriched by spraying 
in petroleum oil, and then used as an illuminant. If used 
as fuel, enriched water gas has a heat value of 500 to 6cx) 
B.t.u. per cubic foot. 

323. Manufacture of water gas. — The essential parts of the 
apparatus are shown diagrammatically in Fig. 116. (i) Air is forced 
by a blower (^1) through the fire in the generator (B), and the hot 
gases pass down the carburetor (C) up into the superheater (D), and 
escape through an opening (not shown) into the air. This operation 
is called the " blow\" It heats the fire brick inside the carburetor 
and superheater intensely hot ; air is often forced in to raise the tem- 
perature. (2) The air valves and the opening at the top of the 
superheater are now closed, and the " run " begins. Steam is forced 
into the generator at the bottom. In passing through the mass of 
incandescent carbon, the steam and carbon interact thus : — 

C + HoO = CO + Ho 

Carbon Steam Carbon Monoxide Hydrogen 

The mixed gases rise to the top of the carburetor, where they meet a 
spray of oil. And as the gaseous mixture passes down the carburetor 
and up the superheater, the hydro- Air 

carbons of the oil are transformed /i:^g^ ^ ^^^^i^ 

by the intense heat into gaseous hy- ^- ^""^"^"^ I^^^ ^^^ 

drocarbons which do not hquefy when '^" 

the final gas is cooled. (3) From ^'-- "7- - Modified Bunsen 

.1 I. 4. 4.1. J. burner used on a stove to 

the superheater the water gas passes 

4.U u ^u T • ^ / 17\ burn coal gas 

through the purifying apparatus (£) 

into a holder. A ton of hard coal yields about 44,000 cubic feet of 

enriched water gas. 

324. Coal gas is made by heating coal in closed retorts 
and purifying the volatile product (326). It is largely 
hydrogen (45 to 50 per cent) and methane (30 to 36 per 
cent) ; other ingredients are hydrocarbons (ethylene, etc.), 
carbon monoxide and dioxide, and nitrogen. It burns 
with a yellow flame. When used as a fuel, considerable 
air is admitted and a special burner is used. In the 
laboratory we use the Bunsen burner (Figs. 126, 127). In 



276 



PRACTICAL CHEMISTRY 



our houses the gas range burner is merely several small 
modified Bunsen burners arranged advantageously (Fig. 
117). The heat value of coal gas varies from 525 to 600 
B.t.u. per cubic foot. 

325. Illuminants. — Some of the gases used as fuel are 




Fig. 118. — Diagram of coal gas plant 

also used as a source of Kght, i.e. as illuminants. Coal 
gas and enriched water gas are the most important. 

326. Manufacture of coal gas. — A diagram of a coal gas plant 
is shown in Fig. 118. (i) The coal is heated several hours in closed 
retorts (A). The volatile products escape from the retorts and 
bubble through water into the hydraulic main (B). Here some of 
the tar is deposited and ammonium compounds are dissolved by the 
water which flows constantly through the main and prevents the gas 
from escaping back into the retorts. The ammoniacai liquor and tar 
flow into the tar well (C). (2) From the hydrauHc main the hot 
and impure gas passes through a long series of vertical pipes called 
the condenser (D), which cools the gas and removes tar. (3) An 
exhauster (E) draws or forces the gas from the condenser into the 
scrubber (and onward through the purifiers into the gas holder). 
(4) The scrubber (F) is a taU tower filled with coke or pebbles over 
which ammoniacai Hquor and water trickle. The object of the scrub- 
ber is to remove the remaining ammonium compounds, and also car- 
bon dioxide, hydrogen sulphide, and the last traces of tar. (5) From 



FUELS — ILLUMINATING GASES — FLAME 277 

the scrubber the gas passes into the purifier (G), which is a series of 
shallow rectangular boxes with frames loosely covered with lime or 
iron oxide, or both. In the purifier any remaining carbon dioxide 
and sulphur compounds are removed. (6) The purified gas next 
passes through a large meter, which records its volume, and then 
into a gas holder from which the gas is forced through pipes to the 
consumer. 

A ton of good gas coal yields about 10,000 cubic feet of gas, 1400 
pounds of coke (287), 120 pounds of tar, 20 gallons of ammoniacal 
liquor (171, 175), and a varying amount of gas carbon (288). 

The tar, or coal tar as it is often called, collected from the hydrauhc 
main and condenser, is a thick, black, foul-smelling liquid. Some is 
used for preserving timber, making tarred paper and black var- 
nishes, and as a protective paint. ]\Iost of it is separated by dis- 
tillation into its important constituents (372). 

327. The illuminating gas flame. — Luminous flames 
are produced when certain gases burn. Let us consider an 
ordinary illuminating gas flame. The gas issues from a 
sht in the burner tip and spreads out in a thin sheet. When 
the gas is ignited, the heat of the burning gases decomposes 
the hydrocarbons into hydrogen and carbon. The hy- 
drogen burns to water. Part of the carbon burns at once 
to carbon dioxide. But some of the fine particles of car- 
bon are heated white-hot and give the flame its illuminating 
power. Eventually all the carbon burns, if sufficient oxy- 
gen is suppHed and the temperature is high enough. 

The flame smokes or deposits free carbon, if the air supply is cut 
off or diminished or the temperature reduced. For example, if a 
bottle is held low dow^n over the flame, smoke is given off ; the same 
result is produced when the flame is cooled. The presence of un- 
burned carbon in the flame can be shown by putting a cold object, 
such as a crayon or glass rod, in or just over the flame ; a deposit of 
soot (carbon) soon gathers. 

■ 

The flame is flattened for two purposes, viz. (i) to ex- 
pose a large surface to the air so that all the carbon will be 



2 78 



PRACTICAL CHEMISTRY 



consumed, and (2) to increase the. amount of light. There 
are two distinct parts, or zones, to this flame (Fig. 119). 
The lower part near the tip is black and consists largely 
of cold, non-luminous gas, while the 
upper part — " the flame " — is yel- 
low-white and contains luminous par- 
ticles of carbon. 



328. Oil gas is an illuminant made from 
petroleum by heating the vapor, or the 
vapor of some distillates, under proper con- 
ditions. The process is similar to cracking 
petroleum (315). The gas burns with a 
brilliant flame. Pintschgas is made from oil. 

329. Illuminating gas. — Coal gas 
is often burned alone but water gas 

is usually mixed with 60 or 70 per cent of coal gas. This 
mixture is called '' illuminating gas." Owing to the high 
percentage of carbon monoxide, water gas and mixtures 
containing it are poisonous (294). 

Illuminating gases are complex mixtures. The accom- 
panying table shows the approximate composition. 

CoMPOSiTiox OF Illuminating Gases (by \'olume) 




Fig. 119. — An Illumi- 
nating gas fiame 



Constituents 


Coal Gas 


Water Gas 


Oil Gas 


Methane 


35 


17 


49 


Illuminants 

Hydrogen 

Carbon Mono.xide 

Carbon Dioxide 


4 
49 

7 

I 


9 
40 

29 

I 


22 

14 
3 

I 


Nitrogen 


4 


^ 


I 



Methane, hydrogen^ and carbon monoxide burn with 
a feeble (non-yellow) flame; they furnish heat, but Httle 
light. The illuminants consist of ethylene (C2H4), acetylene 



FUELS — ILLUMINATING GASES — FLAME 



279 



(C2H2), benzene (CgHe), and other hydrocarbons; they 
burn with a yellow flame (318). 

330. The luminosity of an illuminating gas is measured by a pho- 
tometer and is expressed in candles or candle power. The determi- 
nation is made by comparing the light of the burning gas with the 
light produced by a standard ilame (or a standard wax candle). Or- 
dinary coal gas has about 17 candle power, water gas about 25, and 
oil gas 50 or more. Ordinary illuminating gas has a varying candle 
power (iS to 20), since it is usually a mixture of coal gas and water gas. 
The use of mantles has greatly improved the methods of lighting 
by gas (338). 

331. More about luminous flames. — In an illuminating 

gas flame the gas itself burns in the air. In an oil lamp, 
e.g. kerosene lamp, the oil is drawn 
up through the wick and volatiHzed 
by heat into a gas, which burns ; the 
air supply is increased through small 
holes in the burner (below the flame) 
or in large lamps through a central 
vent also. In many Hghthouses the 
vapor from oil is burned directly {i.e. 
not through a wick). In a candle, 
the heat from the burning wick melts 
and volatilizes the wax, and this gas 
burns. The structure of the lumi- 
nous flame is essentially the same, 
whether produced by burning illuminating gas, kerosene 
oil, or candle wax. 

332. The candle flame is more easily studied than an 
illuminating gas flame, and may be taken as the type. Ex- 
amination of the sketch of an enlarged vertical section 
shown in Fig. 120 reveals four somewhat conical portions: 
(i) Around the wick there is a dark cone (A), filled with 



z>— - 




JB'- 



Fig. 120. — Sketch of 
the parts of a candle 
flame 




28o PRACTICAL CHEMISTRY 

combustible, but unburned gases formed from the melted 
wax. It is possible to draw off these gases through a small- 
bore glass tube and light them. (Compare Fig. 128.) 
(2) Around the lower part of the dark cone is a faint bluish 
cup-shaped part (B, B). It is the lower portion of the 
exterior cone where complete combus- 
tion of the gases occurs, since plenty 
of oxygen from the air reaches this 
portion. (3) Above the dark cone is 
the luminous portion (C) . It is the larg- 
est and most important part of the flame. 
:^. — ch rr d Combustion is incomplete here, because 

paper showing the Httle or no oxygen can pass through the 
hottest part of a exterior cone. The temperature is high, 
ame however, and the hydrocarbons un- 

dergo complex changes. Acetylene is probably formed. 
The most characteristic change is the Hberation of small 
particles of carbon. This liberated carbon, heated to in- 
candescence by the burning gases, makes the flame luminous. 
(4) The exterior cone {D, D) is almost invisible. Here the 
combustion is complete, because oxygen of the air changes 
all the carbon to carbon dioxide. We can show that this is 
the hottest region of the flame by pressing a piece of stiff 
w^hite paper for an instant down upon the flame almost 
to the wick. The paper will be charred by the hot outer 
portion of the flame, as shown in Fig. 121. 

These four portions may be found, more or less easily, in all lumi- 
nous hydrocarbon flames, whatever the shape. In ordinary gas 
flame the luminous part is enlarged, while the blue part cannot be 
seen unless the flame is turned low or looked at through a small 
opening (Fig. 119). 

The gaseous products of the combustion of hydrocar- 
bons, as repeatedly stated, are water vapor and carbon 



FUELS — ILLUMINATING GASES — FLAME 281 




Fig. 122. — Effect of lowering the 
temperature of a candle flame 



dioxide. A bottle in which a candle is burning has, at 
first, a deposit of moisture on the inside ; and if the candle 
is removed and calcium hydroxide solution is added, the 
presence of carbon dioxide is shown by the cloudiness of 
the solution (1). 

We can readily show with a candle flame that the luminosity of 
hydrocarbon flames is affected by temperature. Thus, if a coil of 
copper wire is lowered upon a 
candle flame, the flame smokes, 
loses its yellow color, and finally 
goes out ; but if a coil of hot wire 
is used, the flame burns unchanged 
(Fig. 122). Similarly, if a piece of 
wire gauze is held a few inches 
above a Bunsen burner and the 
gas is turned on and lighted above 
the gauze, the flame will not pass through the gauze until the latter 
becomes hot (Fig. 115). The Davy safety lamp depends on this 
principle (319). 

Xot all luminous flames are hydrocarbon flames. Thus, magne- 
sium burns with a brilliant flame. Its luminosity is due to the in- 
candescence of solid particles of magnesium oxide. Similarly, the 
bright flame of burning phosphorus is accounted for by the incan- 
descent particles of solid phosphorus pentoxide. (See also the 
Welsbach light, 338.) 

333. Acetylene and its flame. — Acetylene (C2H2) is a 
gas, which is prepared by the interaction of calcium car- 
bide and water, thus : — 

CaC2 + H2O = C2H2 + Ca(OH)o 

Calcium Carbide Water Acetylene Calcium Hydroxide 

Prepared in this way, it can be used on a small scale, 
as in a miner's lamp or portable lantern, or stored in 
tanks for Hghting towns or houses. Acetylene dissolves in 
acetone, and cyUnders in which considerable gas has 



282 



PRACTIC.\L CHEMISTRY 



been dissolved are used to furnish gas, e.g. for mining 
camps and other localities where ordinary illuminating 
gas is not available. 

Acetylene burns in the air with a luminous, smoky iiame. 
But when considerable air is mixed with the gas as the 





i 

Fig. 123. — -Acetylene burner and flame 

latter issues from a small opening, the mixture burns with 
a briUiant, white flame, which does not smoke. 

Ordinary gas burners cannot be used for acetylene because the 
flame produces soot. A common form of burner is shown in Fig. 1 23. 
The acetylene as it escapes from the supply pipe (A) into the burner 
sucks in air through the small side holes (B). This mixture, upon 
ignition, burns as a small flat flame at right angles to the 
burner (Fig. 123, right). 




Fig. 124. — Oxy-acetylene torch and flame 

334. The oxy-acetylene flame. — A mixture of acety- 
lene and considerable oxygen burns with an intensely 
hot flame ; a temperature of nearly 3000° C. can be reached 



FUELS — ILLUMINATING GASES — FLAME 2S- 



if the right mixture of acetylene and oxygen is burned in 
a special blowpipe called an oxy-acetylene torch (Fig. -124). 
The thermochemical equation is : — 

2C2H, + 5O2 = 4CO2 + H2O +6o7.52ocal. 

Acetylene Oxygen Carbon Dioxide Water 

Ordinary tools cut hard metal slowly, but the tip of the 
oxy-acetylene flame when 
passed slowly across the 
metal melts (" cuts ") it 
quickly. Metal struc- 
tures, such as fences, 
bridges, frames of build- 
ings, '^ scrapped " war- 
ships, etc., are speedily 
dismantled by this flame. 
The fire department of 
large cities is equipped 
with an oxy-acetylene 
outfit for cutting a pas- 
sage through steel doors 
of vaults or effecting an 
entrance into parts of a 
fireproof building. The 
ox\'-acetvlene flame is 




¥ig. 125. — Welding with an acetylene 
torch. A cracked cylinder of a loco- 
motive is being welded just inside the 
opening in the temporary brick wall 



also extensively used for welding metals (Figs. 28 and 125). 

335. Non-luminous flames. — Some flames are non-luminous, 
i.e. they are colorless, or if colored, the flames do not give enough 
light for use as an illuminant. Thus, the ordinary hydrogen flame 
is almost invisible. The flames of carbon monoxide and methane 
are faint blue. The most common non-luminous flame is the Bunsen 
flame. 

336. The Bunsen burner and its flame. — When illu- 
minating gas is mixed with air before burning, and the mix- 



284 



PRACTICAL CHEMISTRY 



ture burned in a suitable burner, a flame is produced which 
is non-luminous and hot, and deposits no carbon. Such 
a flame is called the Bunsen flame. It was first produced 
in a burner devised by the German chemist Bunsen. This 
burner is used in laboratories as a source of 
heat. The parts of a typical burner are shown 
in Fig. 126. 

The gas enters the base and flows from a 
small opening into the long tube, which screws 
down over this opening. At the lower end of 
the tube and above the inlet are two holes, 
through which air is drawn by the gas as it rushes 
out of the small opening. The gas and air mix 
as they rise in the tube, and the gas burns at 
the top of the long tube. 

The size of the air holes at the bottom can 
be changed by a movable ring. When the 
holes are wide open, the typical non-luminous 
Bunsen flame is formed ; this flame 
is free from soot, and apparatus 
heated by it is not blackened. 
When the holes are closed, the gas 
burns with a luminous flame and 
deposits carbon. 



O 



o 



I 




Fig. 126. — Parts of a typ 
ical Bunsen burner 



The gas burns at the top of the tube and not inside, because the 
proper mixture of gas and air rushes out more quickly than the flame 
can travel back through the tube to the small inlet. If the gas supply 
is slowly decreased, the flame becomes smaller, disappears with a 
slight explosion {" strikes back "), and burns at the small gas inlet 
inside the tube. A sudden draft of air, too much air admitted through 
the holes at the lower end of the tube, or too low gas pressure may 
cause the flame to " strike back." 

This modified flame, which has a pale color, a disagreeable odor, 



FUELS — ILLUMINATING GASES — FLAME 28^ 



aIt, 



and deposits soot, should be extinguished and the proper flame 
produced before further use. 

The Bunsen flame (Fig. 127) has a bluish color and con- 
sists essentially of two cones, which may often be distin- 
guished by the different tints. The 
lower and inner cone consists of air and 
unburned gas. It is bluish, but becomes 
green when too much air is admitted 
(best seen in an imperfect flame). The 
upper and outer cone is the flame proper 
and consists of burning gases. It is 
faint blue and hot (about 1500° C). 
The color is due to the burning mixture 
of carbon monoxide (blue flame) and 
hydrogen (colorless flame). 

The fact that the inner cone consists of un- 
burned gases can be shown by putting one 
end of a small bore glass tube into the cone ; 
gas will rise through the tube and can be ig- 
nited at the upper end (Fig. 128, left). If a sulphur match is sup- 
ported by a pin across the top of an unlighted burner, it will not be- 




Fig. 127. ■ — Sketch 
of a Bunsen flame 





Fig. 1 28. — The cones of a Bunsen flame. Drawing unburned gases from 
the inner cone (left). .\ match does not ignite in the inner cone 
(center). The inner cone produces a dark disk and the outer cone 
a luminous ring (right) 

come ignited until some time after the gas is first lighted (Fig. 12S. 
center). 



r 



286 PRACTICAL CHEMISTRY 

We can readily show that the outer cone consists of burning gases. 
A match held near the side of the flame ignites quickly, while a match 
laid for an instant across the top of the tube is charred only at the 
two points where it touches the outer cone. Finally, a wire gauze, if 
pressed down upon the flame, shows a dark disk surrounded by a 
luminous ring due to the inner and outer cones respectively (Fig. 128, 
right). 

337. Oxidizing and reducing flames. — The outer por- 

, tion of the Bunsen flame 

is called the oxidizing 
flame. Here oxygen 
Fig. 129. - Blowpipe ^^^^ ^^^ ^.^ .g ab-^ndant. 

The inner and lower portion is called the reducing flame. 

Here the excess of unburned hydrocarbons withdraws 

oxygen. A sketch of the general relation 

of these flames is show^n in Fig. 127. 

A is the most effective part of the ^. t., • 

. Fig. 130. — Blowpipe 

oxidizing flame, and B of the reducmg flame. A is the 

flame. At A metals are oxidized, oxidizing part, and 

and at B oxygen compounds are re- ^ ^^^ reducing 
duced. 

Sometimes a tapering tube with a small opening at the bent end, 
called a blowpipe (Fig. 129), is used to produce these flames. A 
special tube with a flattened top is put inside the burner tube to pro- 
duce a luminous flame. The tip of the blowpipe rests in or near this 
flame, and if air is gently and continuously blown through the blow- 
pipe, a long slender flame is produced, called a blow^pipe flame (Fig. 
130). It is like the Bunsen flame as far as its oxidizing and reducing 
properties are concerned. 

338. The Welsbach light. — The Bunsen flame is used 
in producing the Welsbach light. A conical shaped mantle 
consisting of a firm network of thorium oxide (99 per cent) 
and cerium oxide (i per cent) is suspended over a Bunsen 
flame. The heat of the flame makes the mantle glow and 



FUELS — ILLUMINATING GASES — FLAME 287 

give a brilliant light. With equal volumes of gas, the Wels- 
bach mantle gives about four times as much light as an 
ordinary gas burner. There are several kinds of mantles 
(Fig. 131). 




— Making inverted mantles for the Welsbach light 

EXERCISES 

1. Name five fuels and three illuminants. 

2. How is the heat value of fuels (a) measured and (b) stated? 

3. What is the heat value of (a) hard coal, {b) fuel, oil, (c) wood, 
(d) coke ? 

4. Define and illustrate a thermal equation. 

5. Prepare a summary of (a) burning coal, (b) manufacturing 
coal gas, (c) producer gas, (d) water gas, (e) fuel oil. 

6. E.xplain the use of gasolene in an automobile. 

7. Topics for home study : (a) Hydrocarbons, (b) Natural gas. 
(c) Construction of a gas range burner, (d) A gas flame, (e) Manu- 
facture of candles. (/) Acetylene in metal working. 

8. What is the formula of methane, ethylene, he.xane, acetylene? 
What is the weight of a mole of each gas? 

9. Complete: (a) C H = CO; (b) CO + ~ = COo; 

(0 CO2 -f = CO; (d) CH44-— = C02 + ; (e) CaCj 

+ = + Ca(0H)2. 

10. Draw a diagram of the apparatus for manufacturing (a) coal gas, 
(b) water gas, (c) calcium carbide. 



288 PRACTICAL CHEMISTRY 

11. Essay topics: (a) The by-products of coal gas manufacture. 
(b) Manufacture of Welsbach mantles, (c) Illumination in light- 
houses. (See National Geographic Magazine, January, 19 13.) (d) The 
petroleum industry, (e) Fuel oil. 

12. Draw from actual observation a diagram of the parts of (a) a 
candle flame, (b) an illuminating gas flame, (c) a Bunsen flame (showing 
the oxidizing and reducing parts). 

13. Describe a Welsbach burner and light. What is the mantle? 
What is its relation to the light? 

14. Home exercises : (a) Examine a Welsbach burner from which 
the mantle has been removed and compare with a Bunsen burner. 
(b) Examine the burner and flame of a gas cooking range. Compare 
both with a Bunsen burner and flame, (c) Examine a kerosene lamp 
and sketch the burner, {d) Test illuminating gas for sulphur com- 
pounds. (Suggestion. Hold a paper moistened with lead nitrate 
solution in the escaping gas.) 

PROBLEMS 

1. A candle weighing 50 gm. consists of wax composed of 88 per 
cent carbon and 12 per cent hydrogen. What weight of carbon dioxide 
and of water will be formed by burning half the candle? 

2. How many liters of hydrogen and of carbon monoxide at 10° C. 
and 750 mm. will be formed by passing 100 gm. of steam over incan- 
descent carbon? 

3. An acetylene gas plant consumes 100 cubic feet an hour. How 
much calcium carbide would be used in a month of 30 days, if the gas 
is burned an average of 5 hours a day? 

4. What volume of air (containing 21 per cent of ox3^gen by volume) 
will be required for the combustion of 100 tons of coal, assuming that 
the coal is 80 per cent pure carbon and burns to carbon dioxide? 

5. Ten tons of coke were burned and only 35 tons of carbon dioxide 
were produced. Calculate the per cent of carbon in the coke. 

6. Calculate the B.t.u. liberated by burning the following: 
(a) I ton of coke, (b) 1000 lb. of fuel oil, (c) 10,000 cu. ft. of natural gas, 
(d) 2000 cu. ft. of producer gas, (c) the number of cubic feet of illumi- 
nating gas burned in your home for a month (assume 550 B.t.u. per cu.ft.), 
(/) apply (e) to the school building. 



CHAPTER XXTIT 
OTHER CARBON COMPOUNDS 

339. What are organic compounds? — Carbon is an 
essential element in a large number of compounds. Be- 
sides carbon, other elements are hydrogen, oxygen, and 
nitrogen ; sulphur and phosphorus are sometimes found. 
Many carbon compounds form series, just as the hydro- 
carbons do (317). Carbon compounds occur so frequently 
in plants and animals and are so closely associated with 
Hfe processes, they are called organic compounds in con- 
trast to inorganic or mineral compounds which are found 
chiefly in the earth. The branch of chemistry which 
deals exclusively with carbon compounds is called Organic 
Chemistry. In this chapter we shall study a few impor- 
tant organic compounds. 

340. Carbohydrates are composed of carbon, hydrogen, 
and oxygen. Examples are sugar, starch, and cellulose 
(the essential part of wood fiber and cotton fiber). 

341. Sugars. — There are many different sugars. The 
most important is ordinary sugar or cane sugar, which 
is also called sucrose. Other sugars are dextrose, levulose, 
lactose, and maltose. 

342. Sucrose (C12H22O11) is widely distributed. Sugar 
cane contains about 18 per cent and sugar beets from 12 to 
15 per cent, and these are the main source of sucrose. 

Sucrose is a white solid ; rock candy is well crystallized 
sucrose. It is very soluble in water ; one part of water dis- 
solves about three times its weight of sugar at ordinary 

289 



290 PRACTICAL CHEMISTRY 

temperatures. If sugar is carefully heated it melts. As 
the temperature is raised, the sugar begins to decompose ; 
water is given off and a light brown substance called caramel 
is formed, which is used to color soups and gravies. By 




Fig. 132. — Vacuum pans and evaporator in a Cuban sugar mill 

further heating, a black porous mass of carbon is finally 
obtained, often called sugar charcoal. Thus we see that 
sugar consists of carbon, hydrogen, and oxygen. 

343. The manufacture of sugar from sugar cane and sugar beets 
involves two main operations. 

(i) In the preparation of raw sugar from sugar cane the juice 
obtained by crushing the cane is first boiled with a weak calcium hy- 
droxide solution to neutralize acids, remove impurities, and prevent 
fermentation ; carbon dioxide is next added to remove the excess of 
lime ; and the final solution is filtered through bone black. This 
purified juice is evaporated in vacuum pans until the sugar begins 
to crystallize from the cooled liquid (Fig. 132). The liquid is next 
allowed to stand several hours in crystallizing troughs (Fig. 133). 
And the crystals are separated finally from the brown liquid by a 
centrifugal machine (Fig. 134). The Hquid left is molasses. 

In the preparation of raw sugar from sugar beets the beets are 



OTHER CARBON COMPOUNDS 



291 



soaked in water, which dissolves the sugar. The solution is treated 
by processes much like those applied to cane sugar solutions. 

(2) Raw sugar is dark colored, and must be refined before use. 
(a) The raw sugar is dissolved in water, air is blown in to agitate 




rig. i,-,s. — Crystallizing troughs 

the heated solution, and lime and other substances are added to gather 
the impurities into a scum or clot. The colored liquid is filtered, 
first through cloth bags and 



then through animal charcoal. 
(b) The filtered sirup is treated 
as in (i). The crystals are 
dried in a heated tube, called 
a granulator, to form granu- 
lated sugar. 

344. Dextrose (CeHioOe) 
is a white solid about 
three fifths as sweet as 
sucrose. It is very soki- 
ble in water, but crystal- 
lizes from it with diffi- 
culty. Dextrose is found 




Fig. I j4. — Crystallizing troughs (up- 
per row) and centrifugal machines 
(lower row) 



292 PRACTICAL CHEMISTRY 

in honey and in many fruits, especially grapes, and is some- 
times called grape sugar. Another name for it is glucose. 

The thick sirup called commercially by different names (e.g. 
" karo ") contains about 20 per cent of glucose (besides 40 to 45 of 
maltose, and 30 to 35 of dextrine). It is manufactured by heating 
starch with dilute hydrochloric acid; if the process is carried far 
enough the product is a hard, wax-like solid known as commercial 
grape sugar, which is almost pure dextrose. 

Glucose is an inexpensive substitute for sucrose, and 
is extensively used in making candy, jelUes, sirups, and 
other sweet mixtures. 

Levulose (C6H12O6) is a sweet, white solid found in fruits and honey, 
and is often associated with dextrose. It is sometimes called fructose 
or fruit sugar. 

345. Testing for dextrose. — Dextrose and levulose are 
reducing agents. An alkaline solution of dextrose is used 
to reduce a silver solution and deposit the silver as a bright 
film in making reflectors for automobiles, mirrors, Dewar 
flasks, and thermos bottles. Dextrose reduces a strong al- 
kahne mixture of copper sulphate and sodium potassium 
tartrate, known as Fehling's solution. Thus, when this 
solution is boiled with dextrose (or a reducing sugar), a 
reddish copper compound (cuprous oxide, CuoO) is formed. 

346. Isomerism. — The formula of both dextrose and levulose is 
C6H12O6, yet their properties are very different. The difference is 
due to a different arrangement of the atoms in a molecule. Such com- 
pounds are called isomers and illustrate isomerism. There are 
many cases of isomerism among organic compounds. 

347. Lactose (C12H22O11) occurs in milk and is some- 
times called milk sugar. It gives milk its sweet taste. 
Cow's milk contains from 3 to 5 per cent of lactose. Crys- 
tallized lactose is a rather hard, gritty solid, much like 



OTHER CARBON COMPOUNDS 293 

sucrose, though not so sweet or soluble. A solution of 
lactose reduces Fehling's solution. 

Lactose is not fermented by ordinary yeast, but a special ferment, 
called lactic ferment, converts it into alcohol and lactic acid. The 
lactic acid gives milk its sour taste and also assists in curdling the 
milk. i.e. in changing the casein into a clot or curd. Lactose is ob- 
tained from whey, which is the liquid left after the solids have been 
pressed from milk curdled by rennet in the manufacture of cheese. 
Lactose is used in preparing infant foods and certain medicines. 

348. Maltose (C12H22O11) is formed from starch by malt, 
hence the name maltose. The transformation is caused 
by diastase, which is formed in the malt by allowing moist 
barley to sprout in a warm place. Maltose is also formed 
from starch by the ptyalin in the saliva. 

^laltose ferments readily with yeast, forming alcohol and car- 
bon dioxide (see commercial production of alcohol (366)). Like 
lactose, maltose is a sweet solid, very soluble in water, from which 
it forms crystals ; its solution reduces Fehling's solution. 

349. Starch is the most widely distributed and abundant 
carbohydrate. It is found in wheat, corn, and all other 
grains, in potatoes, beans, peas, and similar vegetables, 
and also in rice, sago, tapioca, and nuts. Many parts of 
plants contain starch ; e.g. the stalk, stem, leaves, and 
especially the root, seed, and fruit. The food value of 
vegetables depends largely on the starch they contain. 
Large quantities of starch are consumed as food ; much 
is used in laundries, paper manufactories, and cotton cloth 
mills, and in the manufacture of glucose and adhesives. 

Starch, as usually seen, is a white mass, but it really 
consists of minute grains which vary with the plant, as may 
be seen by examining starch with a microscope (Fig. 135). 



2Q4 PRACTIC.\L CHEMISTRY 

Starch is extracted by a mechanical process from many 
plants — in the United States largely from corn and wheat 
and in Europe chiefly from potatoes, rice, and wheat. 

Starch is only very slightly soluble in water because 
the granules are enveloped in an insoluble membrane of 
cellulose (,352). But if boiled with water, the membrane 



0'^ ^%^^ -^% 




r'^ 



Starch grains (magnified) —wheat (left), rice ^center), 
corn (right) 

bursts, the grains swell, dissolve to some extent, and on 
coohng do not settle out but form a jelly-Hke mass — the 
famihar starch paste. With cold water, starch forms an 
ordinary suspension. WTiereas with hot water, a colloidal 
solution is produced (86. 101). 

Starch gives a blue colored substance when added to 
iodine solution, and its presence in many vegetables and 
foods can be readily shown by grinding the substance in 
a mortar w^th cold water and adding a drop of dilute iodine 
solution. It does not reduce Fehhng's solution. 

Starch is a complex carbohydrate and its composition corresponds 
to the formula (CeHioOo)^- Starch is readily transformed into other 
carbohydrates. Thus, it forms maltose and dextrin (348. 351) ; 
with dilute acids it forms maltose, dextrin, and dextrose (344). An 
equation for the change of starch into dextrose is : — 

(C6Hio05)x + •vH.O = .v(C6Hi,0e) 

Starch Water Dextrose 

350. Making bread. — Wheat flour contains about 70 
per cent of starch. The remainder is chiefly water and 



OTHER CARBON COMPOUNDS 295 

gluten, though small qucintitics of mineral matter and fat 
are present. In making bread, the flour, water, and yeast 
are thoroughly mixed into dough, which is put in a warm 
place to rise. Fermentation begins at once. Fermentation 
is the conversion of an organic compound, like starch or 
some sugars, into simpler compounds by the action of cata- 
lytic substances called enzymes, e.g. diastase and ptyalin. 
Enzymes from the yeast change starch into dextrose, 
or a similar fermentable substance, which undergoes fer- 
mentation, forming alcohol and carbon dioxide. The 
gases escape in part through the dough, which becomes 
Kght and porous. When the dough is baked, the heat stops 
the action of the enzymes ; but the alcohol, carbon dioxide, 
and some water escape and pufT up the mass still more. 
The heat, however, soon hardens the starch, gluten, etc., 
into a firm porous loaf. 

351. Dextrin (CsiHgoOsi probably) is a light brown, or white, sweet- 
ish solid formed by heating starch to 2oo°-25o° C. It dissolves in cold 
water and forms a sticky solution which is used as an adhesive, es- 
pecially on postage stamps. It is also used in making mucilage, for 
thickening colors and sticking them to cloth in calico-printing, and as 
an ingredient of candy and beverages. 

When starched clothes are ironed the hot iron changes some of the 
starch to dextrin, which gives a gloss to the fabric. Dextrin is also 
formed from starch when bread is baked or toasted. 

352. Cellulose ((C6HioOo)i) is the substance of which 
the cell walls of plants consist, and is therefore very widely 
distributed. Wood contains cellulose and related com- 
pounds, while cotton, linen, and the best quahties of filter 
paper are nearly pure cellulose. 

Pure cellulose is a white substance, insoluble in most 
liquids, but soluble in a mixture of ammonia and copper 
hydroxide. Sulphuric acid of a special strength, if quickly 



296 



PRACTICAL CHEMISTRY 



and properly applied to paper, changes it into a tough form 
called parchment paper. The latter is often substituted 
for animal parchment {e.g. sheepskin). 

353. Derivatives of cellulose. — With nitric acid cellulose forms 
cellulose nitrates. One of these is gun cotton. It looks like ordinary 
cotton, and may be spun, woven, and pressed into cakes. It burns 
quickly, if unconfined, but when ignited by a percussion cap or when 
burned in a confined space, gun cotton explodes violently. It is used 
in blasting and for torpedoes and submarine mines. 

A mixture of gun cotton, ether, and alcohol soon becomes a plastic 
mass, which upon being rolled and carefully dried forms a trans- 
parent solid; this substance is called smokeless powder. When 
exploded, it forms carbon dioxide and monoxide, nitrogen, hydrogen 
and water vapor — all colorless gases. 

A solution of certain cellulose nitrates in a mixture of alcohol and 
ether is called collodion. When collodion is poured or brushed upon 

a glass plate or the skin, the 
solvent evaporates, leaving 
behind a thin film. It is 
used in preparing photo- 
graphic films and as a coat- 
ing for wounds. 

A mixture of camphor 
and cellulose nitrates is 
called celluloid, which is 
widely used in making photo- 
graphic films. 

354. Paper consists 
chiefly of cellulose mat- 
ted together. Most 
paper, especially that 
used for nev^^spapers, is 

made from wood. Considerable v^riting paper, however, 

is still made from cotton and linen rags. 

In making paper from wood, the latter is first reduced to a pulp 
mechanically by grinding the wood upon a revolving stone or chemi- 




Fig. 136. — A bcalcr full of pulp which 
is being separated and cut into fine 
particles 



OTHER CARBON COMPOUNDS 



297 



cally by heating it under pressure with sodium hydroxide or calcium 
bisulphite (acid calcium sulphite). The pulp is carefully washed, 
bleached, and washed again. It goes next to the beater (Fig. 136) 
in which revolving knives separate and cut the fibers of cellulose into 
finer particles. Here the filler (clay), sizing (rosin), and coloring 
matter (if desired) are added and thoroughly mixed with the pulp. 
Sometimes this mixture is further treated in a refiner. The pulp is 
then suspended in a large volume of water (go to 96 per cent) and 
the thin mixture is pumped to the Fourdrinier machine on which 
the sheet is made (Fig. 137). The pulp mixture flows on to a fine, 




Fig. 137. — A Fourdrinier machine for making paper 

wire cloth which moves slowly along ; the water drains of! and leaves 
the fibers on the wire as a thin moist layer, which is dried and pressed 
by rollers into a compact sheet. The sheet finally consists mainly 
of interlaced fibers of cellulose. 



355. Alcohols consist of carbon, hydrogen, and oxygen. 
Some properties of methyl alcohol (CH3OH) and ethyl 
alcohol (C2H5OH) have been described and their use as 
fuels has been stated (285, 314). Methyl and ethyl alco- 
hols mix with water in all proportions. Ordinary com- 
mercial ethyl alcohol contains 4 to 5 per cent of water. 
Absolute alcohol is 100 per cent ethyl alcohol. Denatured 
alcohol is essentially a mixture of 100 parts ethyl alcohol^ 



298 PRACTICAL CHEMISTRY 

10 parts methyl alcohol, and a small proportion of some 
poisonous, or unpalatable, substance, such as benzene, 
pyridine, or kerosene. (There are many legal formulas 
of denatured alcohol.) This mixture is impossible for 
use as a beverage, but is suitable for industrial processes. 

Denatured alcohol and methyl alcohol are not taxed ; ethyl al- 
cohol is. Owing to this tax the price of ethyl alcohol is high. Hence 
its use as a fuel is very much restricted. 

Ethyl alcohol is used in manufacturing varnishes, cel- 
luloid, collodion, artificial silk, extracts, perfumes, ether 
((C2H5)20), chloroform (CHCI3), iodoform (CHI3), and 
numberless other organic compounds. 

356. Manufacture of ethyl alcohol. — Ethyl alcohol is manufac- 
tured by the fermentation of certain sugars obtained from molasses 
or from starch. When yeast is added to a solution of dextrose, mal- 
tose obtained from starch by action of diastase (348), or any other 
fermentable sugar, complex chemical changes occur ; the main prod- 
ucts resulting from the action of the enzyme zymase (from the yeast) 
upon dextrose and maltose are alcohol and carbon dioxide, thus : — 

CfiHtoOe = 2C0H5OH + 2CO2 
Dextrose Alcohol Carbon Dioxide 

CioHooOu + H2O = 4C2H5OH -f 4CO2 

The alcohol, which constitutes about 15 per cent of the final mix- 
ture, is separated by fractional distillation. 

357. Acetic acid (C2H4O2 or CH3.COOH) is the most 
common organic acid. It is manufactured on a large scale 
by the dry distillation of wood (285). The distillate, which 
is called pyroligneous acid, contains about 10 per cent of 
acetic acid, besides methyl alcohol, and acetone (367). 

Very concentrated acetic acid is called glacial acetic 
acid. Commercial acetic acid contains about 30 per cent 
of pure acetic acid. It is a rather weak acid (247). Acetic 



OTHER CARBON COMPOUNDS 299 

acid is used to prepare acetates, dyestuffs, medicines, and 
white lead. Some of its salts — the acetates — are useful 
compounds, e.g. lead acetate and Paris green. 

358. Vinegar is dilute acetic acid, containing from 4 to 6 per cent 
of the acid. It is prepared by oxidizing dilute alcohol (by the action 
of bacteria) ; the essential chemical change is : — 

C2H5OH -h Go = C0H4O0 + HoO 

Alcohol Oxygen Acetic Acid Water 

The alcohol is usually obtained from sugars. Substances containing 
starch or fermentable sugars, e.g. fruit juices, cider, and molasses, 
slowly ferment when exposed to the air (which always contains bac- 
teria necessary for the chemical transformations), forming alcohol 
first and finally vinegar. Cider vinegar is made this way. 

359. Other organic acids. — Rhubarb and sorrel con- 
tain a salt of oxalic acid (C2H4O2). This acid is poisonous. 
The acid and some of its salts decompose iron rust and 
inks containing iron, and are often used to remove such 
stains from cloth. The acid is also an ingredient of 
mixtures used to clean metals and straw. Lactic acid 
(CsHeOs) occurs in sour milk (347). When sour milk 
is used in cooking, the baking soda (HXaCOa) and 
lactic acid interact, producing soluble sodium lactate 
and carbon dioxide gas ; the gas puffs up the dough. 
Malic acid (C4H6O5) is found free or as salts in apples, 
pears, cherries, currants, gooseberries, rhubarb, grapes, 
and berries of the mountain ash tree ; also in the 
roots, leaves, and seeds of many vegetables. Tartaric 
acid (C4H6O6) occurs as the potassium salt (acid potassium 
tartrate, HKC4H4O6) in grapes and other fruits. During 
the fermentation of grape juice, the impure salt is deposited 
in the wine casks. From this argol or crude tartar the 
acid is prepared. Purified argol is called cream of tartar ; 



300 PRACTICAL CHEMISTRY 

it is an ingredient of baking powder. Citric acid (CeHgOy) 
occurs abundantly in lemons and oranges, and in small 
quantities in currants, gooseberries, raspberries, and other 
acid fruits. The acid is used in making lemonade. (For 
other organic acids, see 361.) 

360. Esters are compounds of carbon, hydrogen, and 
oxygen closely related to alcohols and organic acids. For 
example, ethyl alcohol and acetic acid form the ester called 
ethyl acetate, thus : — 

C2H5.OH + CH3.COOH = CH3.COOC2H5 + H2O 

Ethyl Alcohol Acetic Acid Ethyl Acetate Water 

Ethyl acetate has a pleasant, fruitlike odor. Its for- 
mation in this way is a simple test for alcohol or acetic acid. 
Ethyl acetate is analogous to sodium acetate, i.e. the organic 
salt contains the radical ethyl (C2H5), whereas the metallic 
salt contains sodium. 

Organic acids form many important esters. Some occur in fruits 
and flowers, and in many cases give the fragrance and flavor. Others 
are manufactured, and used as the characteristic ingredient of flavor- 
ing extracts, perfumery, and beverages. Ethyl butyrate has the 
taste and odor of pineapples, amyl acetate of bananas, amyl valerate 
of apples, and methyl salicylate of wintergreen. 

361. General relations of fats, glycerin, and soap. -- 

Natural fats and oils are essentially mixtures of three esters, 
called glyceryl stearate, glyceryl palmitate, and glyceryl 
oleate. Their common names are stearin, palmitin, and 
olein. Stearin and palmitin are solids at ordinary tem- 
peratures ; olein is a hquid. Hard fats are largely stearin 
and palmitin; soft or liquid fats and oils are largely olein. 
The organic acids corresponding to these esters are stearic 
acid (C18H36O2), palmitic acid (C16H32O2), and oleic acid 



OTHER CARBON COMPOUNDS 301 

(Ci8H340-j). The corresponding alcohol is glycerin 
(C3H5(OH)3). The radical of glycerin is glyceryl (C3H5). 
Hence the names glyceryl stearate, etc. 

When fats are heated with very hot steam or with sul- 
phuric acid, they are changed into glycerin and the cor- 
responding acids. Thus, with stearin the change is : — 

(Ci7H35COO)3C3H5 + 3H2O = C3H5(OH)3 + 3C17H35.COOH 

Stearin Glycerin Stearic Acid 

But if fats are boiled with sodium hydroxide or a similar 
alkaU, glycerin and an alkahne salt of the corresponding 
acid are formed, thus (for stearin) : — 

(Ci7H35COO)3C3H5+3NaOH = 3Ci7H35COOXa + C3H5(OH)3 

Glyceryl Sodium Sodium Glycerin 

Stearate Hydroxide Stearate 

Soap is a mixture of such alkaline salts (365). In a few 
words, the general relations are these : (i) fats are esters ; 
(2) treated with steam or acid, fats form glycerin and or- 
ganic acids ; (3) treated with alkalies, fats form glycerin 
and soap. 

362. Natural fats and oils are often complex mixtures. The 
chief ingredients, however, are stearin, palmitin, and olein ; small 
quantities of similar esters are usually present and often give certain 
fats characteristic properties. Tallow is about 66 per cent stearin 
and palmitin and ^7, per cent olein; it is a solid fat obtained from 
the sheep and ox and is used in making soap and candles. Lard 
consists of olein, stearin, palmitin, and a Httle linolein ; it is obtained 
from the fat of the hog and is used in cooking. Olive oil, which is 
obtained from the fruit of the oHve tree, contains about 72 per cent 
of olein (and a similar fat) and about 2S per cent of stearin and pal- 
mitin, together with small quantities of other substances ; the best 
qualities are used as salad oil, while cheap kinds are utilized in cooking, 
as a lubricant, and for making soap. Cottonseed oil is similar to olive 



302 PRACTICAL CHEMISTRY 

oil ; it is obtained from the seeds of the cotton plant and is used ex- 
tensively in cooking, as salad oil, and as a substitute for other oils. 
Butter fat is 60 per cent olein, 30 per cent stearin and palmitin, 
and 5 per cent butyrin (glyceryl butyrate), together with small quan- 
tities of esters corresponding to capric, caprylic, and myristic acids. 
The pleasant flavor of butter is mainly due to the esters and some other 
substances that are present in small proportions. Oleomargarine 
and other substitutes for butter resemble real butter. They are made 
from different fats and oils {e.g. cocoanut oil). 

363. Hydrogenation of oils. — Oils, such as cottonseed oil, when 
heated, mixed with finely divided nickel, and then treated with hy- 
drogen under pressure, become solid fats. The chemical change con- 
sists in the addition of hydrogen. For example, olein becomes stearin, 
thus : — 

(Cl7H33COO)3C3H5 + Ho = (CnH35COO)3C3H5 

Olein Hydrogen Stearin 

The chemical change is called hydrogenation. The nickel acts as 
a catalyst, and is removed by filtering the melted fat. Substitutes 
for lard and other solid fats are made by this process, e.g. " crisco " 
from cottonseed oil. Fish oils are also converted into soap stock. 

364. Glycerin (CsHgOs) or (C3H5(OH)3) is a thick, sweet, 
colorless liquid. It absorbs water from the air and is often 
added to substances to keep them moist, e.g. stamping 
ink. When heated, it decomposes and gives off irritating 
fumes, like those produced by burning fat. It is used to 
make nitroglycerin and printers' ink rolls ; it is also used 
as a sweetening ingredient of certain foods, tobacco, and 
candy; cosmetics and lotions often contain glycerin. 

Glycerin is often called glycerol. It is an alcohol, and when 
treated with a mixture of concentrated nitric and sulphuric acids, 
it forms an ester commonly known as nitroglycerin (C3H5(ON02)3). 
This is a slightly yellow, heavy, oily liquid. It is the well-known 
explosive. When kindled by a flame, it burns without explosion; 
but if subjected to a shock or heated suddenly by a percussion cap, 
it explodes violently. Nitroglycerin is used in blasting; but since 
it is dangerous to handle and transport, it is usually mixed with some 



OTHER CARBON COMPOUNDS 



303 



porous substance, such as infusorial earth, fine sand, clay, or even 
sawdust. In this form, it is called dynamite. Other explosives 
contain nitroglycerin, e.g. blasting gelatin and cordite. 

365. Manufacture of soap. — Soap is made by boiling 
fats with sodium hydroxide solution. This process is called 
saponification. Sodium hydroxide produces hard soap, 
consisting chiefly of sodium palmitate, sodium stearate, 
and sodium oleate. 

Most soaps are made by boiling the fat and alkali in a huge kettle 
(Fig. 138). This operation produces a thick, frothy mixture of soap, 




Fig. 138. — Soap kettle filled with a boiling mixture of fat and 
sodium hydroxide 



glycerin, and alkali. At the proper time salt is added, thereby caus- 
ing the soap to separate and rise to the top. The liquid beneath is 
drawn off, and from it glycerin is extracted. 

Some soaps are boiled again wdth rosin or cocoanut oil, and then 
mixed (if desired) with perfume, coloring matter, or filling material 
(such as sodium silicate, sand, or borax). Floating soaps are made 
by forcing air into the semi-solid mass before cooling. The best soaps 
are prepared so that the finished product will not contain any un- 
changed fat or " free alkali," i.e. sodium hydroxide. 

The cleansing action of soap is ascribed to two causes: (i) Soap 
hydrolyzes, i.e. interacts, with w^ater — especially hot water — and 



304 PRACTICAL CHEMISTRY 

the liberated alkali (sodium hydroxide) acts upon the grease and oil 
that is usually mixed with the dirt. (2) Soap causes fat and grease 
to form an emulsion (86) ; the microscopic globules remain suspended 
in water and can be readily washed off with the dirt. The second 
cause is the more efficient. 

366. Formaldehyde (CH2O) is a gas with an irritating 
odor. The gas dissolves in water. The commercial solu- 
tion sold as formalin contains 40 per cent of formaldehyde. 
It hardens tissue and is used as a preservative in museums. 
It is a convenient and efficient disinfectant and antiseptic. 
When so used, the solution is vaporized in a special appara- 
tus and the vapors conducted into the infected room. A 
solid called para-formaldehyde is sometimes used to dis- 
infect. When heated, it decomposes into formaldehyde. 
Para-formaldehyde candles are often used in place of sul- 
phur candles (Fig. 95). 

367. Acetone (CsHgO) is a colorless liquid which has an ethereal 
odor. It boils at about 56° C. It is used as a solvent for fats, oils, 
and waxes, and in the preparation of cordite and various smokeless 
powders and certain organic compounds {e.g. chloroform). Acetone 
is one of the products obtained by the distillation of wood (285). 

368. Ethyl ether (ordinary ether, (C2H6)20) is a colorless, 
volatile liquid, with a pecuHar, pleasing taste and odor. 
It boils at 35° C, and the vapor is very inflammable. The 
liquid should never he brought near a flame. It is a good 
solvent for waxes, fats, oils, and other organic compounds. 
Its chief use is as an anaesthetic to produce unconscious- 
ness in surgical operations. Ether is manufactured by 
heating a mixture of ethyl alcohol and sulphuric acid. 

369. Chloroform (CHCI3) is a heavy hquid made from 
alcohol (or acetone) and bleaching powder. It is used as 
an anaesthetic in special cases. 



OTHER CARBON COMPOUNDS 305 

370. Iodoform (CHI3) is a yellow solid made from iodine, 
alcohol (or acetone), and an alkali. It is widely used as 
an antiseptic for drcssin.c^ wounds. 

371. Carbon tetrachloride (CCI4) is a heavy liquid. It 
is made by passing chlorine into carbon disulphide, thus : — 

3CI, + CS2 = CCI4 + S2CI2 

Chlorine Carbon Carbon Sulphur 

Disulphide Tetrachloride Chloride 

It is used to extract fats, grease, and gums from seeds, bones, 
and wool. Certain mixtures {e.g. " carbona") used for 
cleansing fabrics contain carbon tetrachloride. When 
heated it forms a heavy non-combustible vapor, and is used 
in small hand fire extinguishers {e.g. " pyrene," Fig. 66) ; 
it is especially useful in extinguishing fires due to gasolene. 

372. Coal tar (326) yields important compounds by 
distillation. Benzene (CeHe) and toluene (CyHg) are 
liquids ; naphthalene (doHg) and anthracene (C14H10 ) are 
solids. These hydrocarbons are indispensable, being the 
parent substances of dyes, medicines, and explosives. 
Naphthalene is called moth balls and is used as a substitute 
for camphor. Phenol (CeHsOH) or carbolic acid is a white 
solid obtained from coal tar. It is used extensively as a 
disinfectant, especially in the form of a weak solution. 

EXERCISES 

1. How would you show in the laboratory that carbon is a con- 
stituent of (a) carbohydrates and (b) alcohol? 

2. Discuss the distribution of sucrose. State its properties. Does 
cane sugar diflfer from beet sugar? 

3. Compare dextrose and levulose. How are these sugars related 
to sucrose? 

4. What is the test for dextrose and similar sugars? 

5. Describe the manufacture of raw sugar. How is raw sugar 
refined? 

6. What is (a) lactose and (6) maltose? Why is each so named? 



3o6 PRACTICAL CHEMISTRY 

7. What is (a) methanol, (b) absolute alcohol, (c) denatured 
alcohol? 

8. Define and illustrate by means of sugars (a) hydrolysis and 
(6) fermentation. 

9. How would you show that a leaf contains starch? 

10. Topics for home study : {a) Dextrin, (b) Cellulose — its 
properties and derivatives, (c) The chemistry of bread-making. 
(d) The manufacture of paper, (e) Flour. (/) Alcohol, (g) En- 
zymes, (h) Glucose. (0 Manufacture of soap. 

11. State the general relations of fats to glycerin. 

12. Name several fats. What is (a) lard, (b) olive oil, (c) butter? 

13. Discuss fully the chemistry of soap. 

14. What is (a) ethyl acetate, (b) formaldehyde, {c) acetone, 
(d) iodoform, (e) ether, (/) phenol, (g) carbon tetrachloride? State 
a specific use of each. 

15. Name five organic acids and state the source of each. 



CHAPTER XXIV 

FOOD AND NUTRITION 

373. What are the functions of food? — The different 
kinds of food we eat perform two main functions. First, 
they supply materials needed for the growth, maintenance, 
and repair of the body. Second, they provide energy 
necessary to keep the body at the proper temperature, as 
well as to enable us to move about and perform our 
work. These functions are sometimes condensed by 
saying food supphes the body with building material and 
fuel. 

374. What are nutrients ? — The parts of the food that 
nourish the body are called nutrients. And the complex 
process by which the nutrients become of use is called nu- 
trition. Nutrients are chiefly derived from three groups 
of organic compounds, viz. carbohydrates, fats, and pro- 
teins. Water and inorganic substances, i.e. mineral mat- 
ter, though not nutrients are vitally connected with nutri- 
tion. 

375. Uses of nutrients. — Carbohydrates and fats undergo 
chemical changes in the body and thereby provide 
energy. They are fuel foods. Both may also become 
transformed to some extent into a reserve supply. For 
example, carbohydrates may be stored in the liver in the 
form of glycogen and fats are often deposited in the form 
of protective tissue. 

On the other hand proteins are body builders, i.e. they 
furnish material to replace worn-out muscle and nerve 

307 



3o8 PRACTICAL CHEMISTRY 

tissue. They differ from carbohydrates and fats in being 
composed partly of nitrogen. Foods which contain pro- 
tein are lean meat, eggs, milk, cheese, peas, beans, and grains 
like wheat (the cereals). 

376. Function of water and mineral matter. — Water and mineral 
matter do not build tissue or furnish energy. Nevertheless both are 
indispensable for life processes. Water makes up about 70 per cent 
of the weight of the body. It keeps the tissues soft and pliable, 
dissolves juices and digested food, and assists in eliminating poisonous 
matter from the body. 

Whereas mineral matter makes up only about 4 per cent of the 
weight of the body and consists of compounds of the following 
elements (in order of abundance) : Calcium, phosphorus, potassium, 
sulphur, sodium, chlorine, magnesium, iron (and minute quantities of 
iodine, fluorine, and silicon). (Compare 11.) These elements supply 
the materials for the rigid parts of the body. e.g. bones and teeth. 
They furnish acids, bases, salts, and organo-metallic compounds, 
which give many fluids and juices of the body vital properties. Hy- 
drochloric acid of the gastric juice and the hematin of the red blood 
corpuscles are examples of necessary mineral matter. 

Mineral matter is obtained from seasoning added to food and from 
vegetables and fruits. 

377. Composition of foods. — The proportion of carbo- 
hydrates, fats, proteins, and mineral matter varies greatly 



■eWater 35. 



Protein 9.2 
Fat 1.3 



. Carbo- 
hydrates 53.1 



<- Water 87.0 



-Protein 3.4 
.Carbc- 
hyiirates 5.0 



WHITE BREAD MILK 

Fig. 139. — Composition of bread and milk 

in different foods. The average composition (in per cent) 
of the edible portion of some common foods is shown in 
the accompanying Table of Composition of Foods, and 
also in Fig. 139. 



FOOD AND NUTRITION 

Table of Composition of Foods (in Per Cent) 



309 



Foods 



Apples .... 
Bacon .... 
Beans (dried) . . 
Beefsteak (sirloin) 
Butter .... 
Cheese (cream) 
Codfish (fresh) , 
Corn (green) . , 

Eggs 

Grapes .... 
Ham (smoked) 
Mutton (forequarter) 
Oatmeal . 
Peanuts . 
Potatoes . 
Rice . . 
Tomatoes 
Walnuts (English) 



Water 


Carbo- 
hydrate 


Fat 


Protein 


84.6 


14.2 


0-5 


0.4 


20.2 


— 


64.8 


9.9 


12.6 


59-6 


1.8 


22.5 


61.9 


— 


18.5 


18.6 


II. 


— 


85.0 


I.O 


34-2 


2-4 


33-7 


25-9 


82.5 


— 


0-3 


16.3 


75-4 


19.7 


I.I 


3-1 


73-7 


— 


lOo 


14.8 


77-4 


19.2 


1.6 


1-3 


40-3 


— 


38.8 


16.1 


52.9 


— 


30.9 


15-3 


7-3 


67.5 


7.2 


16. 1 


9.2 


24.4 


38.6 


25.8 


78.3 


18.4 


O.I 


2.2 


12.3 


79.0 


0-3 


8.0 


94-3 


3-9 


0.4 


O.Q 


2-5 

i 


16. 1 


63-4 


16.6 



.Mineral 
Matter 



03 
5-1 
3-5 
1.0 

30 
3-8 
0.9 
0.7 
1.0 

0-5 
4.8 
0.9 
1.9 
2.0 
1.0 
0.4 
0.5 
1-4 



378. Food as a source of energy. — The food we eat 
undergoes complex chemical changes in the body. These 
changes take place at first in the digestive organs and con- 
stitute the process called digestion. The digested food, 
which is in a liquid or dissolved form, is absorbed and trans- 
ported to the various parts of the body, where it is built 
up into the tissue of which the various organs consist. 

Sooner or later the tissue undergoes oxidation or some 
related process. Oxygen for this purpose comes from 
the air we breathe into the lungs ; here the oxygen is 
taken up by the blood and distributed to the organs and 

' .\ fuller table can be found in Bulletin 28 (Revised) or Farmers' 
Bulletin 142, United States Department of Agriculture, Office of Ex- 
periment Stations. 



3IO PRACTICAL CHEMISTRY 

muscles of the body. The tissue is slowly transformed 
by the oxygen into carbon dioxide and water (27). 

Heat is liberated by these chemical changes. New tissue 
is, of course, built up from the digested food. We might 
call food a fuel, because its digested products are oxidized, 
just as fuels are oxidized when they burn. The heat 
producing power of food is called its fuel value. And 
just as different fuels differ in the amount of heat lib- 
erated per pound, so various foods differ in their fuel 
value. 

379. Fuel value of food. — The heat value, i.e. fuel 
value, of food is determined in the same way as the heat 
value of fuels, viz., by burning a weighed quantity of the 
food in a bomb calorimeter and measuring the amount of 
heat liberated (301. 302). The unit used in measuring the 
fuel value of food is the Calorie. This is the amount of 
heat that will raise the temperature of i kilogram of water 
i°C. 

The food we eat, however, is not all digested nor is the 
nutritive portion completely transformed in the body. 
So the heat values of uneaten food obtained by the bomb 
calorimeter must be changed a little to account for these 
losses. These corrected fuel values are called physiological 
fuel values. They are the fuel values of the part of the 
food that is actually transformed into energy in the body 
— the real fuel value of the food digested and transformed. 
The physiological fuel values are the ones usually meant 
when the term fuel value is used. 

The fuel value of food is often stated in Calories 
per pound, i.e. the number of Calories furnished by one 
pound of food. The fuel values of the foods tabu- 
lated in 377 are shown in the Table of Fuel Value of 
Foods. 



FOOD AND NUTRITION 311 

Table of Fuel Vall-e of Foods (Calories Per Pound) 



Apples . . 


. 290 


Codfish . . 


• 325 


Oatmeal . 


. i860 


Bacon . . 


. 2840 


Corn . . . 


• 470 


Peanuts . 


. 2560 


Beans . 


. 1605 


Eggs . . . 


. 720 


Potatoes . 


. 385 


Beefsteak . 


• 1130 


Grapes . . 


• 450 


Rice . . 


• 1630 


Butter. . 


• 3491 


Ham . . . 


. 1940 


Tomatoes . 


• 105 


Cheese . 


• 1950 


Mutton . . 


• 1595 


Walnuts . 


■ 3-^85 



380. How much food do we need? — The amount of 
food needed varies with many factors, e.g. weight, work, 
age, and sex. A growing boy needs more than his father, 
a football player more than one who watches the game, 
and a hard laborer more than one who has a sedentary 
occupation. An adult who does moderate muscular work 
needs enough food to yield from 2500 to 3000 Calories a 
day. A satisfactory division w^ould be : — 

Carbohydrate 400-500 gm., or 1600-2000 Cal. 

Fat 70-85 gni., or 630-765 Cal. 

Protein 7 5-80 gm., or 300-320 Cal. 

The fuel value of food is only part of the story. 
Sugar or butter would furnish enough heat, but a diet con- 
sisting largely of carbohydrates or fats would not repair 
worn-out tissue. We should eat food containing protein, 
as well as carbohydrates and fat. Authorities agree that 
an adult who does moderate muscular work needs 75-80 
grams (3 ounces) of protein per day. If more is eaten, 
it is partly consumed as fuel and partly rejected by the 
body. 

381. How to select an adequate diet. — The usual tables 
of composition and fuel value do not enable us to select the 
prepared food that is needed for an adequate diet. By 
means of the accompanying Table of Servings of Food it 



312 



PRACTICAL CHEMISTRY 



is easy to arrange several sets of daily menus which will 
include the approximate amount of protein and furnish 
sufficient fuel value. By learning the protein content 
and fuel value of the important items, or those used fre- 
quently, you can readily tell if your diet is adequate. 

Table of Servings of Food 



FOOD 



Weight in Grams 



Apple, baked 

Apple, raw 

Apple sauce (3 heaping Tbs.) 

Banana, raw 

Beans, baked 

Beans, lima ...... 

Beets (4 heaping Tbs.) . . 
Biscuit (3 baking powder) 
Bread, white (2 slices) . . . 
Butter 

Cheese (i cu. in.) . . . . 

Chicken, creamed (on toast) . 

Cocoa, I cup 

Codfish cakes (2) . . . . 

Corn chowder (1.5 cups) . . 

Cream of wheat 

Cream toast (i slice) . . ■ 

Currant jelly (i h. Tbs.) . . 

Custard (2 heaping Tbs.) . . 

Doughnut (i) 

Dressing, French (2 ts.) 

Fgg (i) 

Figs (5) 

Fish chowder (i cup) . . 

Fish, stuffed and baked 

Gingerbread (2.5 cakes) . 

Hominy (i cup) .... 

Ice cream (2 heaping Tbs.) 
Lamb, roast (i slice) . . 
Lettuce, 4 leaves .... 
Macaroni and cheese (i cup) 



Average 
Serving 



135 

150 

125 

194 

185 

75 

200 

go 

76 

15 



230 
132 
333 
250 
148 

37 
134 

37 
9 

50 
100 
284 
152 
100 

245 
100 

QO 



Protein Fat 



I 

0.5 
0.2: 

1-5 
19 

5 
5 
8 

6.5 

0.2 
6 




19 
10 

5 
1 1 



2-5 



6., 

4 
38 
33 

6 

3 

5 
20 

I 
10 



I 
0.8 



13 

13 
6 

3 
10 

I 
II 



6 

0.3 
10 

4 

7 



Carbo- 
hydrate 



14 



26 
16 

47 
28 

47 
20 

15 
45 
40 



22 
12 
17 
39 
33 
49 
28 

19 
20 



73 
30 
7 
69 
32 
18 



32 



Total 
Calories 



117 

70 
198 
125 
345 
100 

80 

311 
200 
118 
87 
273 
122 
171 
286 
161 

339 
114 
176 
162 

63 

80 

309 

362 

196 

363 
140 
182 

323 
8 

294 



FOOD AND NUTRITION 



313 



FOOD 



Maple sugar (i cake) . 
Milk and sugar for cereal 
Milk, glass ... 
Onions, boiled 

Orange 

Orange ice (2 heaping Tbs 
Pie, apple ih) .... 
Potato, baked . . 

Potato, boiled . . 

Potato, sweet .... 

Pot roast 

Prunes (5) 



Pudding, chocolate farina 
Pudding, cottage . . 
Pudding, rice . . . 
Rice, steamed (i cup) . 
Salad, fruit .... 
Salad, potato .... 
Salad, vegetable . . . 
Sandwich, chicken . . 
Sandwich, ham . 
Shredded wheat (i) . . 
Snow pudding (2 heaping Tbs.) 
Soup, cream of celery (i cup) 
Soup, cream of tomato (i cup 
Spinach (i heaping Tbs.) . 
Steak, Hamburg (i cake) . 
Vegetable hash .... 



Weight in Grams 



Average 

Serving 



100 

73 
220 

85 

100 

126 
130 



141 
144 
133 

200 

262 

150 

157 

70 

70 

2Q 
80 

100 

50 
140 



Protein 



2 

7 

2 

1-5 

I 

4 
4 
4 
3 
41 
I 

7 
6 
6 
4 

4 

3 

9 

7 

3 

4-5 

3 

3 

16 
9 



Fat 



2 

9 

03 
0.3 
12 



I 

4 
10 

0.5 

9 

9-5 

4 

8 



Carbo- 
hydrate 



83 
15 
I I 
10 
21 

75 
54 
32 
31 

42 

63 
33 
77 
34 
40 
46 

31 
16 
22 

~7 
23 
12 

5 

6-5 
3 

36 



Total 
Calories 



332 
86 
153 
48 
93 
307 
340 
144 
140 
200 
272 
256 
223 
422 
223 
176 
201 
140 

^5 
160 
226 
108 

66 
113 

i23 

56 
136 



382. We need an adequate diet. — To fulfill its functions 
our food should be carefully chosen. The carbohydrates 
and fats must be in the right quantity for fuel value and 
the protein in the proper proportion for tissue building. 
Moreover, we ought to select the three classes of nutrients 
from a wide variety of foods in order to provide a mixed 
diet, obtain the right kind of protein, and secure indispen- 
sable mineral matter. We should drink water freely — 



314 PRACTICAL CHEMISTRY • 

at least six glasses a day. We should eat regularly an abun- 
dance of vegetables and cereals, which furnish bulky in- 
gredients and assist the elimination of waste matter ; they 
also yield mineral matter. Certain foods should alw^ays 
form a part of our diet, e.g. leaf vegetables, milk, whole 
wheat, unpolished rice, and fruit juices because they pro- 
vide minute quantities of certain substances called vita- 
mins, which are essential to growth and good health. 

Finally, we ought not to forget that properly selected 
food must be well digested and assimilated by the body. 
Nutrition is a complex process. If we wish to have strong, 
healthy bodies, we must not only choose our food carefully, 
but masticate it well, and rest during the first part of the 
digestive process ; we must also exercise regularly and 
estabhsh early in life good habits of body and mind. 

EXERCISES 

1. Prepare a summary of this chapter. 

2. Define the terms food, nutrition, and nutrients. 

3. Xame the three groups of nutrients. Give three examples of 
each. 

4. Learn the composition and fuel value of (a) bread, {b) butter, 
(c) potatoes, (d) eggs, (e) milk. 

5. Select from the table in 377 foods rich in (a) protein, (b) carbo- 
hydrate, and (c) fat. 

6. Topics for home study : (a) Digestion, (b) Water and nutri- 
tion, (c) Enzymes and digestion, (d) Mineral matter in. the body, 
(g) Respiration. (/) The blood, (g) Cost and fuel value of food. 
{h) Bomb calorimeter. 

7. Discuss the topics: (a) Food is a source of energy, (b) The 
body resembles a steam engine. 

8. Assuming that one square inch represents looo Calories, draw 
diagrams of the fuel value of five foods from the table in 379. 

9. Use the table in 381 for the following : (a) Make out a menu 
for breakfast, dinner, and supper which contains 75-So g"^. of protein 
and furnishes 2500-3000 Cal. (b) As in (a) for 100 gm. of protein and 
about 3500 Cal. (c) As in (a) for 100 gm. of fat, 85 of protein, and 
about 4000 Cal. 



FOOD AND NUTRITION 315 

10. Use the table in 381 to keej) a record (or make an estimate) of 
the approximate amount of carbohydrate, fat, and protein you eat in 
(a) one day, (/') three days, {c) one week, {d) one lunch. 

PROBLEMS 

1. By means of the table in 379 and prices obtained from your 
grocer compute (a) the number of Calories of 10 of the items that may 
be bought for 20 cents. (6) As in (a), compute the cost of 100 Cal. of 
the same items. 

2. Calculate the weight of (a) mineral matter in i lb. of cheese, 
{b) water in c lb. of potatoes, (c) fat in i lb. of beefsteak, (d) protein in 
I lb. of beans, (c) water in i lb. of butter, (/) carbohydrate in i lb. of 
oatmeal. 

3. (a) What weight of bacon is needed to furnish as much fat as 
I lb. of butter? (b) Of tomatoes to provide the carbohydrate in i lb. 
of potatoes? (c) Of oatmeal to equal the protein in i lb. of beans? 



CHAPTER XXV 

SILICA — SILICATES — GLASS — SILICON — CARBORUNDUM 

383. Occurrence of silica. — The element silicon does 
not occur free in nature, but its compounds are very abun- 
dant and widespread, especially silica and the silicates. 
Sand is chiefly sihca, while clay and most rocks consist 
of one or more silicates. Ordinary soil contains more or 
less silica. Sihcon (through its compounds) makes up 
about one fourth of the earth's crust (11), being next to 
oxygen in abundance. 

Silica is the most abundant and important compound 
of silicon. It is also called silicon dioxide (SiOo). Sand, 
gravel, sandstone, quartzite, and the nu- 
merous varieties of quartz are almost 
wholly silicon dioxide ; many rocks, e.g. 
granite and gneiss, contain silica as an 
essential ingredient. 

Quartz is the commonest form of sili- 
con dioxide. Pure quartz is colorless 
140. — Quartz and transparent, and is called rock 
"•^^^^ crystal. It is crystalline and is fre- 

quently found as single crystals which have a six-sided 
pyramid at one or both ends ; the crystals are some- 
times distorted (Fig. 140). 

There are many varieties of quartz, which differ in color and struc- 
ture. Among the crystalline varieties are the clear, colorless rock 
crystal, the purple amethyst, and the rose, yellow, glassy, milky, 
and smoky forms. Varieties imperfectly crystalline are the waxlike 

316 




SILICA — SILICATES 



317 




chalcedony, the various forms of agate having difTercnt colored layers, 
the reddish brown carnelian, the bhick and white onyx, the red or 
brown jasper, the brown or black flint. 

Opal is a beautiful variety of silica containing varying per cents 
of combined water. Petrified or siHcified wood is the remnant of 
wood in which the 
fiber has been replaced 
by silica. There is a pet- 
rified forest in Arizona. 
Infusorial or diatoma- 
ceous earth (also called 
Tripoli powder) is 
largeh' silica and con- 
sists of the skeletons of minute organisms called diatoms, many be- 
ing of delicate and beautiful structure (Fig. 141). 

384. Properties of silica. — Most varieties of silica are 
hard and brittle, and melt only at a high temperature. 
E.g. quartz is harder than other common substances, breaks 
into fragments with sharp edges, and melts in the oxy- 
hydrogen flame or the electric furnace. If pure silica is 
fused with certain precautions, the viscous mass can be 



Fig. 141. — Diatom shells (enlarged) 






Fig. 142. — Apparatus made from fused silica for use in the laboratory 



drawn into elastic threads, which are used to suspend deli- 
cate parts of electric instruments ; it can also be shaped 
into tubes, flasks, crucibles (Fig. 142), and even large 
pieces of apparatus used in industrial processes. 

Apparatus of fused silica has a low coefhcient of ex- 
pansion, i.e. it expands or contracts only a very Uttle within 



3i8 PRACTICAL CHEMISTRY 

a wide range of temperature. Thus, a silica crucible, un- 
like a porcelain one, will not crack if heated and plunged 
into cold water. It also resists the action of many chem- 
icals. These properties make siUca apparatus very useful 
in the laboratory and chemical manufactories. 

The different forms of silica do not dissolve in water. 
Nor are they attacked by acids, except hydrofluoric acid, 
which transforms them into a volatile fluoride (sihcon tetra- 
fluoride, SiF4). They are converted into soluble sihcates 
when boiled in water containing alkaline substances or 
when fused with the hydroxide or carbonates of sodium 
and potassium. Thus, when fine sand is fused with sodium 
carbonate the equation for the reaction is : — 



SiOo + XaoCOs = 


= NasSiOs 


+ CO2 


Silicon Sodium 


Sodium 


Carbon 


Dioxide Carbonate 


Silicate 


Dioxide 



385. Uses of silica. — Sandstone and quartzite are used 
as building stones, and some varieties of sandstone are 
shaped into grindstones and whetstones. Imm.ense quan- 
tities of sand are used to make glass, porcelain, cement, 
and mortar. Different grades of sand are used as grinding 
and poUshing material in making sandpaper. Glass is 
polished by rubbing it with fine wet sand ; it is also rough- 
ened and cut by blowing or " blasting " fine sand against 
it. Glass stoppers for bottles used in the laboratory are 
" ground " with sand. Many of the varieties of quartz 
are cut and polished into ornaments and gems. 

Infusorial earth (383) is used as a pohshing powder for 
metals (" electro-sihcon " being the commercial name of 
one kind), and in making scouring soaps, cement, soluble 
glass, and refractory brick; owing to the hollow struc- 
ture of its minute particles, considerable is used as an 



SILICA - SILICATES 319 

absorbent of nitroglycerin in the manufacture of dyna- 
mite. 

386. Silicates are salts of silicic acid. There are several 
silicic acids, but only two are well known and easily pre- 
pared, viz. metasilicic acid (H2Si03) and orthosilicic acid 
(H4Si04). The salts of these and other silicic acids are 
among the most common substances in the earth's crust. 

Most rocks consist wholly or largely of silicates of the metals 
aluminium, iron, calcium, potassium, sodium, and magnesium. Some 
common silicates are slate, asbestos (i\Ig3Ca(Si03)4), feldspar 
(KAlSisOs), mica, hornblende, clay (H2Al2(Si04)2.H20), beryl, garnet, 
serpentine (I\Ig3Si207.2H20), and talc (H2Mg3(Si03)4). The lava 
ejected by volcanoes consists largely of fused silicates. 

Naturally occurring silicates are insoluble in water. But 
they decompose very slowly through the joint action of 
water and carbon dioxide. Even the moist carbon dioxide 
in the air slowly decomposes silicates. As a result of this 
gradual but very extensive chemical change, hard rocks 
like granite disintegrate. The more soluble products {e.g. 
sodium and potassium carbonates) are washed aw^ay and 
the less soluble ones such as clay, sand, and iron compounds, 
are left behind. This transformation, which is called 
weathering, is assisted by the mechanical action of water, 
especially alternate freezing and thawing. 

The decomposition of silicates by the joint action of carbon dioxide 
and water (i.e. by carbonic acid (H2CO3)) is due to the fact that 
silicic acid is a weak acid. This property is strikingly shown by the 
formation of basins and terraces of silica in Yellowstone National 
Park. The hot waters of some of the springs in the Park contain 
dissolved alkaline silicates {e.g. NaoSiOs) which are transformed to 
silicic acid by the moist carbon dioxide of the air. The silicic acid, 
which is left where the waters overflow, gradually loses water and 
builds up a deposit of silica, often very beautiful. Silica thus de- 
posited is called geyserite. 



320 



PRACTICAL CHEMISTRY 



387. Sodium silicate. — When fine sand and sodium 
carbonate are fused together, sodium siUcate (Na2Si03) 
is formed. (See equation at end of 384.) Sodium sih- 
cate is a glassy solid, which under special conditions dis- 
solves in water ; hence this silicate is sometimes called 
water glass. SiUcate of soda is the name given to com- 
mercial solutions of varying composition. These solu- 
tions have different properties adapted to special uses. 
Certain brands are used as the adhesive in making the cor- 




Fig. 143. — Making 4-ply paper board used for cartons, shipping con- 
' tainers, and wall board. The two center strips are coated on both 
sides with sodium silicate solution ; the upper and lower strips on 
one side only. All four strips are united firmly together by pressure 
rolls. This machine is one of the largest in use and turns out over 
200 feet of finished board per minute 



rugated paper board, fiber board, and wall board which 
are made into cartons, tubes, trunks, and containers of 
various kinds (Fig. 143). Another brand is used as a 
binder in abrasive wheels, stove and furnace cements, and 
linings. Still another use is as a protective coating 
for wood, paper, and concrete, a fireproof coating or 
ingredient of wood and fabrics, and preservative coating 



SILICA — SILICATES 321 

for eggs ; the last use is due to the fact that the deposit 
of siUcate in the pores of the shells keeps out the air and 
thus prevents the eggs from spoiHng. Finally, considerable 
is used in many chemical processes, e.g. the manufacture 
of certain laundry soaps, sizing of paper, refining of oil, 
and removing paint. 

388. Silicic acids. — When hydrochloric acid is added 
to sodium silicate solution, a white jelly-like precipitate 
called siUcic acid is formed, thus : — 



NaaSiOs 


+ 2HCI = 


HoSiOs 


+ 


2NaCl 


Sodium 


Hydrochloric 


Silicic 




Sodium 


Silicate 


Acid 


Acid 




Chloride 



Under certain conditions probably the precipitate is 
a mixture of meta- and ortho-silicic acids (HaSiOs and 
H4Si04). These acids are closely related. The ortho- 
acid passes into the meta-acid upon drying, thus : — 

H4Si04 = HsSiOa + H2O 

Orthosilicic Acid Metasilicic Acid Water 

And metasilicic acid when heated decomposes into silicon 
dioxide and water, thus : — 

HsSiOs = Si02 + H2O 

Metasilicic Acid Silicon Dioxide Water 

Silicon dioxide may be regarded as the anhydride of meta- 
silicic acid, though contrary to the usual rule this acid can- 
not be formed from the anhydride (Si02) and water (262). 

389. Colloidal acid. — Sodium silicate and hydrochloric acid do 
not always interact as described in 388. If the sodium silicate solu- 
tion is dilute, or the hydrochloric acid is concentrated or in excess, or 
the mixing is done quickly, then the silicic acid which is formed remains 
in solution. This solution, however, is not a solution of the gelatinous 



322 PRACTICAL CHEMISTRY 

silicic acid described above, for the latter is insoluble in water. The 
silicic acid in the solution is in the colloidal state. It cannot be 
filtered out through paper in the usual way. (86, 101, 349.) 

390. Silicon. — Silicon is manufactured by heating sand 
with coke in an electric furnace, thus : — 

SiOo + 2C = Si + 2CO 

Silicon Dioxide Carbon Silicon Carbon ^lonoxide 

Thus prepared, silicon is a brittle, gray-black, lustrous, 
metallic looking solid. It melts at about 1400° C. The 
specific gravity is about 2.37. It is hard enough to produce 
scratches on glass, being almost as hard as quartz. 

Silicon at high temperatures combines with oxygen, though not 
readily, to form silicon dioxide (SiOo). With other elements it forms 
compounds often called silicides, e.g. carbon silicide (CSi). Chlorine 
and elements related to it, especially fluorine, combine with silicon 
to form volatile compounds. Sodium hydroxide and potassium 
hvdroxide interact with silicon, thus : — 



2NaOH -f 


Si + 


HoO ■■ 


= NaoSiOg 


+ 2H, 


Sodixim Hydroxide 


Silicon 


Water 


Sodium Silicate 


Hydrogen 



Most acids produce little or no effect upon silicon, hydrofluoric acid 
being the main exception. 

391. Uses of silicon. — Silicon is made into vessels and parts of 
apparatus designed to withstand the action of acids and other liquids. 
Some is used in the steel industry to remove the gases {e.g. oxygen) 
that cause small holes. An alloy of silicon and iron called ferro- 
silicon is also used for the same purpose. An alloy of iron and silicon 
(14-15 per cent), called duriron, is hard and brittle; it resists the 
corrosive action of acids, especially nitric acid, and is extensively 
used in acid plants. 

392. Silicon carbide or carborundum (SiC). — This 
carbide is a crystallized solid, which varies in color from 
white to brownish-green or black. It is extremely hard. 



SILICA — SILICATES 323 

being nearly as hard as diamond. It is very resistant. 
Acids do not affect it, but potassium hydroxide and some 
other alkaUes do. The extreme hanhiess of carborundum 
has led to its extensive application as an abrasive, and large 
quantities are made into a great variety of grinding wheels, 
whetstones, and polishing cloths. 

Carborundum is manufactured by fusing a mixture of sand (silicon 
dioxide. SiOj) and coke (carbon, C) in an electric furnace similar in 
form to that used in the manufacture of graphite (Fig. 100) and 
silicon. The mixture of sand and coke (to which salt and sawdust 
are added to contribute to the fusion and porosity) is packed around 
the core of granulated coke. The heat generated by the resistance of 
the carbon core to the passage of the powerful current of electricity 
produces a chemical change essentially as follows : — 

SiOo + 3C = SiC + 2CO 

Silicon Dioxide Carbon Silicon Carbide Carbon Monoxide 

393. Other silicon compounds. — When hydrolluoric acid inter- 
acts with silicon dioxide, silicates, or sihcon, silicon tetrafluoride 
(SiF4) is formed. With silicon dioxide the equation is : — 

SiOs + 4HF = SiF4 + H,>0 

Silicon Dioxide Hydrofluoric Acid Silicon Tetrafluoride Water 

Sihcon tetrafluoride is a colodess gas which fumes in moist air owing 
to interaction with water. The equation for the reaction is : — 

3SiF, + 4H0O = H4Si04 + 2HoSiF6 

Silicon Tetrafluoride Water Silicic Acid Hydrofluosilicic Acid 

The hydrofluosilicic acid (sometimes called fluosilicic acid) remains in 
solution, while the (ortho)silicic acid is precipitated. The formation 
of the white gelatinous silicic acid when the gases from the inter- 
action of hydrofluoric acid and a compound of silicon are led into 
water is often used as a test for silicon. 

394. Glass is essentially a mixture of silicates and silica. 
Ordinary glass, such as that used for bottles and window- 
panes, is made by heating sand, calcium carbonate, and 



324 PRACTICAL CHEMISTRY 

sodium carbonate to a high temperature. The product is 
a mixture of calcium siUcate (CaSiOs), sodium silicate 
(NaoSiOs), and silica (Si02). The composition might be 
represented as Na^O, CaO, 6Si02. Sodium-calcium glass 
is called soft glass because it softens readily when heated. 

Other varieties can be made by substituting other sub- 
stances, wholly or partly, for the calcium and sodium com- 
pounds. Thus, potassium carbonate (with calcium car- 
bonate) produces a hard glass which melts at a much higher 
temperature than ordinary sodium glass. 

If a lead compound is used in place of calcium carbonate, 
flint glass is produced which refracts Hght to a high degree ; 
it is used to make lenses for optical instruments, and shades 
for gas and electric lights. On account of its briUiancy 
this glass is made into cut glass vessels for ornaments and 
table use. The design is traced on the glass, cut out by 
a revolving wheel, and the vessel is then poHshed with a 
very fine abrasive. 

Another kind of glass, used extensively for chemical ap- 
paratus and certain cooking utensils, contains a large excess 
of siUca together with boron oxide (B2O3) and aluminium 
oxide (AI2O7). It is made by heating together sand, borax 
(Na2B407), and aluminium oxide. This glass is tough and 
has a much lower coefficient of expansion than ordinary 
glass ; hence it does not break readily with sudden changes 
of temperature. Its trade name is "pyrex." 

Besides the fundamental ingredients, mentioned above, carbon, 
sodium sulphate (Na2S04), sodium nitrate (NaNOs), arsenic tri- 
oxide (AS2O3), and manganese dioxide (Mn02) are used to accomplish 
specific results. For example, manganese dioxide is added to neu- 
tralize the green color due to iron compounds (present as an impurity 
usually in the sand). Cheap glass bottles and jars are green because 
the impurities are not removed. Selenium produces the red glass used 
in railroad and steamship lanterns and in automobile tail lights. 



SILICA — SILICATES 



325 



White glass is made by adding lluorspar (CaF-j), cryolite (NasAlFg), 
stannic oxide (SnO..), or calcium phosphate (Ca3(P04)2). 

395. Manufacture of glass. — The ingredients needed 
for the different varieties of glass (394) are mixed in the 
proper proportions and heated in a furnace or in large 
clay vessels to a high temperature. 
The substances interact and form a 
heavy, viscous semi-fluid. It is 
plastic over a considerable range of 
temperature, and can be poured 
into molds, rolled into sheets, and 
fashioned into various shapes by 
blowing, pulHng, pressing, or stamp- 
ing. 

Bottles and jars of all kinds are 
blown by complicated machines. 
Special or ornamental objects are 
blown into a mold. A skilled work- 
man gathers a mass of the plastic 
glass on the end of a long tube, 
called a glass blowpipe, blows the 
glass into a preliminary shape, lowers 
it into a mold, and blows until the 
mold is filled. In Fig. 144 a work- 
man is shown about to Hft an elec- 
tric Hght bowl from a mold. 

Window glass and other kinds of 
flat glass are made by machinery. In one process the 
glass is blown into a long cylinder (Fig. 145, upper) which 
is allowed to cool ; the ends are then cut off, the cylinder 
is sKt lengthwise, heated until it softens and opens, and 
then rolled out flat. In another process the mixture of 
the raw materials is put into one end of a furnace, melted, 




Fig. 144. — The last 
stage (opening the 
mold) in blowing an 
electric light bowl 



326 



PRACTICAL CHEMISTRY 





Fig. 145. — Making flat ghss. Upper — a huge cylinder of glass on a 

frame about to be slit open lengthwise 
Lower — removing a sheet of glass from an automatic sheet glass 

machine. The raw materials enter at one end and the sheets of 

glass are cut off at the other 



SILICA — SILICATES 327 

and transformed into glass. The viscous mass is passed 
along (in the same machine) to a device which sticks to 
it, pulls it forward between rolls, through a cooling 
chamber, and finally out upon a table where the glass 
is automatically cut into sheets. In Fig. 145 (lower), 
a workman is shown taking off a sheet of glass. 

Plate glass, which is used for windows and wind shields, 
is made by pouring the molten glass upon a large table, 
rolling it with a hot iron, and finally grinding and polish- 
ing the cooled sheet on a rotating table until the surfaces 
are parallel. 

Glass must be cooled slowh". otherwise it will crack or crumble 

to nieces when jarred or scratched. This slow cooling is called 



Fig. 146. — Bottles just coming from an anneahng chamber 

annealing. It is accomplished by passing the objects on a slowly 
moving frame through a chamber in which the temperature is gradu- 
ally lowered (Fig. 146). 

EXERCISES 

1. In what compounds is siHcon found in nature? What propor- 
tion of the earth's crust is sihcon? Compare with other elements. 



328 PRACTICAL CHEMISTRY 

2. Summarize the properties of silica. 

3. Describe the formation, state the uses, and enumerate the proper- 
ties of water glass. 

4. Starting with silicon, how would you prepare successively 
silicon dioxide, sodium silicate, silicic acid, silicon dioxide, silicon? 

6. Topics for essays and discussion: (a) Diatoms, their formation, 
deposition, and uses. (/>) Manufacture of glass, (c) Quartz, (d) Sil- 
icon dioxide as an abrasive, (e) Wire glass. 

6. State the preparation, properties, and uses of carborundum. 

7. Why is sand usually found at the sea shore? Why is sand often 
used to extinguish a small fire? 

PROBLEMS 

1. Calculate the per cent of silicon in (a) orthosilicic acid, (b) meta- 
silicic acid, (c) potassium feldspar (KAlSisOg). 

2. How much sodium silicate can be made from looo kg. of sand? 

3. Write the formula of (a) silicon chloride, (b) silicon 
bromide, (c) cupric silicide, (d) cuprous silicide, (e) sodium metasilicate, 
(/) sodium orthosilicate, (g) magnesium metasilicate, (//) magnesium 
orthosilicate, (/) aluminium metasilicate, (j) ferrous orthosilicate. Cal- 
culate the per cent of silicon in any three of these compounds. 

4. Scheele found that 0.6738 gm. of silicon tetrachloride gave 
2.277 gm. of silver chloride. Calculate the atomic weight of silicon. 
(Equation is SiCU + 4AgN03 + 2H2O = Si02 + 4AgCl + 4HNO3.) 

5. Silicon hydride (SiH4) burns in air. Write the equation, 

6. How much silicon can be made (a) by reducing a ton of sand 
(90 per cent pure) with C; (b) from 119 gm. of potassium silico-fluo- 
ride? (Equation is KsSiFg + 4K = Si + 6KF.) 

7. How much carborundum could be made by using (a) a ton of 
carbon (98 per cent pure) and (b) a ton of sand (95 per cent pure) ? 

8. Calculate the simplest formulas corresponding to (a) Si = 35-897, 
H = 2.564, O = 61.538; (b) Si = 29.166, H = 4-i66, O = 66.666. 
What is the name of each compound? 



CHAPTER XXVI 

CLASSIFICATION OF THE ELEMENTS — METALS AND 
NON-METALS — PERIODIC CLASSIFICATION 

396. Classification of the elements. — In the preceding 
chapters emphasis was laid on different elements, e.g. oxy- 
gen, hydrogen, chlorine, nitrogen, carbon, and sulphur; 
others were mentioned, e.g. sodium, potassium, calcium. 
These elements differ from one another in many ways. But 
some of them are quite similar in their chemical behavior 
and can be put into the same class. The arrangement 
into classes helps us in studying chemistry. 

397. Metals and non-metals. — The elements have 
long been divided into two classes called metals and non- 
metals. At first those elements were called metals which 
were hard, lustrous, heavy, and good conductors of heat, 
whereas the others were called non-metals. This clas- 
sification has been retained, though it is not entirely 
correct. A few metals are not heavy. Moreover certain 
elements act as metals under some conditions and as non- 
metals under other conditions. 

A better classification is based on the ionic theory. Ac- 
cording to this theory, metallic elements form positive 
ions and non-metallic elements negative ions. The only 
exception is hydrogen; this element is classed as a non- 
metal although its ions are positive (H+). In the accom- 
panying Table of Important Metals and Non-metals the 
common elements are put in the usual class. 

329 



330 



PRACTICAL CHEMISTRY 

Table of Important Metals and Non-Metals 



Metals 


Non-metals 


Sodium 


Magnesium 


— 


Hydrogen 


Oxygen 


Potassium 


Zinc 


Chromium 


— 


Sulphur 


— 


Cadmium 


— 


Boron 


— 


Copper 


Mercury 


Manganese 


— 


Fluorine 


Silver 


— . 


— 


Carbon 


Chlorine 


Gold 


Aluminium 


Iron 


Silicon 


Bromine 





— 


Cobalt 


— 


Iodine 


Calcium 


Tin 


Nickel 


Nitrogen 


— 


Strontium 


Lead 


— 


Phosphorus 


(Aluminium) 


Barium 


(Arsenic) 


Platinum 


x\rsenic 


— 




Antimony 




(Antimony) 


(Tin) 




Bismuth 






(Chromium) 
(Manganese) 



398. Periodic classification of the elements. — In 1869 
the Russian chemist Mendelejeff (Fig. 147) pubHshed the 

periodic classification of 
the elements. It is based 
on a relation between the 
properties of the elements 
and their atomic weights. 
The schema of the 
classification is substan- 
tially as follows : If the 
elements beginning with 
helium are arranged in 
the order of their in- 
creasing atomic weights, 
a series results in which 
similar or closely related 
elements occur at inter- 
Fig. 147. - Mendelejeff (1834-1907) vals. That is, the series 




CLASSIFICATION OF THE ELEMENTS 



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PRACTICAL CHEMISTRY 



breaks up into several periods, and the classification is 
called periodic. 

If the series is divided into these periods and the periods 
are placed below each other, the accompanying table is ob- 
tained in which the elements can be viewed in three ways : 
first as a long consecutive series, second as groups, and 
third as periods. The groups are in the vertical columns 
and are designated by the numerals to VIII ; the groups 
(except Group 0) are subdivided into families. The periods 
are in horizontal rows and are numbered from i to 12. 

399. Groups and families. — An examination of the 
elements in the groups shown in the vertical columns of the 
periodic table reveals two interesting facts. First, ele- 
ments which resemble one another are found in the same 
group. Second, in a given group certain elements are more 
closely related than others, giving rise to sub-groups or 
families. In some of these famihes the similarity of the 
members is very marked, e.g. the sodium family (Li, Na, K, 
etc.) and the halogen family (F, CI, Br, I). 

For convenience, the elements described (or mentioned) 
in this book are arranged here as groups or families. 

Group 0. Inert elements or argon family — helium, neon, argon, 
krypton, xenon, niton. 

Group I. Alkali metals or sodium family — lithium, sodium, 
potassium. 

Univalent heavy metals or copper family — copper, silver, 
gold. 

Group II. Alkaline earth metals or calcium family — calcium, 
strontium, barium, radium. 

Bivalent heavy metals or zinc family — magnesium, zinc cad- 
mium, mercury. 

Group III. Boron family — boron. 

Earth metals or aluminium family — aluminium. 

Group IV. Quadrivalent non-metals or carbon family — carbon, 
silicon. 



CLASSIFICATION OF THE ELEMENTS 7,1,7, 

Quadrivalent metals or tin family — tin, lead. 
Group V. Quinquivalent non-metals and metals or nitrogen 
family — nitrogen, phosphorus, arsenic, antimony, bismuth. 

Group VI. Hexavalent metals or chromium family — chromium, 
tungsten, uranium. 

Hexavalent non-metals or oxygen family — oxygen, sulphur. 
Group \'II. Manganese family — manganese. 

Halogen elements or chlorine family — fluorine, chlorine, bro- 
mine, iodine. 

Group \'III. Iron family — iron, cobalt, nickel. 
Platinum family — platinum. 

This arrangement should be examined carefully and re- 
ferred to constantly as the different elements are studied. 
By comparing the periodic table with the table of metals 
and non-metals we see that related elements have been 
grouped in the same way (397). 

400. Periods, properties, and atomic weights. — The 
elements in the same horizontal row in the periodic table 
belong to the same period. The periodic variations of the 
properties of the same typical elements may be illustrated 
by periods 2 and 3. Ignoring the argon group (Group 0\ 
which is somewhat anomalous, and beginning with lith'um, 
the general chemical properties vary with increasing atomic 
weight. 

Let us consider this point in detail. The metallic char- 
acter typified by hthium gradually diminishes through beryl- 
lium and boron ; while the feeble non-metalhc character 
typified by carbon becomes more marked as we pass on 
through nitrogen and oxygen until it reaches a maximum 
in fluorine. The next element is sodium, in which metallic 
properties reappear ; its place therefore is beneath lithium, 
at the beginning of period 3. Proceeding from sodium, 
the same decrease of metalhc and increase of non-metallic 
properties is noticed until potassium is reached, and here 



334 PRACTICAL CHEMISTRY 

again a marked metallic element reappears and period 4 
begins. Hence sodium comes under lithium, magnesium 
under beryllium, aluminium under boron, carbon under 
silicon, and so on through chlorine to potassium, which 
comes under its closely related element sodium. 

There is no sudden change in properties until we pass 
from one period to the next. Thus, fluorine at the end of 
period 2 forms a strong acid, but sodium at the beginning 
of period 3 forms a strong base. Similarly, chlorine is 
strongly acidic, but potassium, which is the first metal in 
the next period, is markedly basic ; chlorine is a typical 
non-metal, while potassium is a typical metal. 

401. The periodic law. — Not all the periods are as 
typical as those just cited. Nevertheless a careful and com- 
prehensive study of all the elements shows that in most 
cases their properties vary periodically with the atomic 
weight. Mendelejeff summarized these facts in the 
periodic law, thus : — 

The properties of the elements are periodic functions of 
their atomic weights. 

The term function as used here means the exhibition 
of some special relation, viz. that of properties to atomic 
weight. It is not beheved now that the relation emphasized 
by Mendelejeff is sufficiently accurate to be called a law. 
Interpreted freely, the facts at the basis of the periodic 
classification mean: (i) properties and atomic weights 
are related ; and (2) this relation is exhibited in very many 
instances at regular intervals. 

402. Defects in the periodic classification. — Examination of 
the periodic table shows imperfections. For example, there are gaps. 
These probably correspond to elements not yet discovered. Three 
such gaps which were in the original table have been filled. When 
Mendelejeff proposed his arrangement, he predicted the discovery 



CLASSIFICATION OF THE ELEMENTS 335 

of three elements having definite properties. These elements — 
gallium, scandium, and germanium — were soon discovered, and 
now occupy their predicted places in the table. Possibly other gaps 
will be tilled by newly discovered elements as was done in the case of 
the zero group. Several elements are out of place, e.g. argon, iodine, 
and tellurium. Hydrogen also lacks an acceptable place. 

403. How can we use the periodic table? — The table 
is a little contusing unless we hrst look for famiUes of re- 
lated elements. For example, we have already studied 
the zero group (124-127). We shall study fluorine, chlo- 
rine, bromine, and iodine — the halogen family — in the next 
chapter. Similarly, we find the family containing nitrogen, 
phosphorus, arsenic, antimony, and bismuth. Nitrogen has 
already been studied, and we shall soon take up the others 
(Chapter XXVUI). Other families of related elements 
to be studied are sodium and potassium (Chapter XXIX), 
and copper, silver, and gold (Chapters XXXIII, XXXVI). 
So by studying the table we can find families of related 
elements. 

Second, we should notice that elements having similar 
properties are near each other. The active metals are in 
Group I (the sodium family) and the less active in Group II. 
Whereas the active non-metals are in Group VII (the chlo- 
rine family) and the less active are in Group VI. Generally 
speaking the active metals and non-metals are at opposite 
ends of the table. This may be re-stated in another way, 
viz. the typical electropositive elements (those that form 
positive ions) are in Group I and the typical electronegative 
elements (those that form negative ions) are in Group VI 
— at opposite ends of the table. 

Third, we can use the table in learning atomic weights. 
Since the elements are arranged in the table in the order 
of their increasing atomic weights, we can soon learn the 



336 PRACTICAL CHEMISTRY 

names of the light elements, heavy elements, and, in time, 
the atomic weight of the important intervening elements. 
Fourth, the table is useful in learning the valence of 
the elements. Elements in the same group usually have 
the same valence. A comparison of the elements in typical 
periodic groups (I, II, VII) with the valence tables in 221 
shows much agreement. 

EXERCISES 

1. State the general physical properties of metals and non-metals. 
What is the characteristic chemical behavior of a metallic element and 
a non-metallic element? 

2. Memorize the names of the important metals and non-metals. 

3. What metals are related to (a) sodium, (b) lead, (c) copper? 

4. As in Exercise 3, what non-metals to (a) carbon, (b) chlorine, 
(c) nitrogen, (d) sulphur? 

5. Classify the following metals and non-metals : aluminium, Zn, 
Na, silicon, Ca, Cu, bismuth, Pb, Ag, C, manganese, O, H, iron, K, Au, 
N, hydrogen, CI, Br, boron, I, S, P. 

6. What is meant by (a) period, (b) group, (c) family? 

7. Illustrate the periodic classification by two periods. 

8. Commit to memory the names of the elements in the following 
families: (a) Argon, (b) sodium, (c) copper, (d) calcium, (e) zinc, 
(/) nitrogen, (g) chlorine, (h) iron. 

9. Topics for essays or discussion : (a) Mendelejeff. (b) Atomic 
weights and properties, (c) Review of valence. 

PROBLEMS (Review) 

1. Calculate the per cent of oxygen in (o) water, (b) potassium chlo- 
rate, (c) nitric acid, (d) lime, (e) silica. 

2. A candle in burning forms 13.21 gm. of carbon dioxide and 
5.58 gm. of water. How much weight did the candle lose? What 
volume of oxygen at 0° C. and 760 mm. was required? 

3. What volume of air (free from carbon dioxide and water vapor) 
contains i gm. of nitrogen? 

4. What weight of sulphur is contained in 500 cc. of SO2? 

5. Suppose 50 1. of nitrous oxide are decomposed iuto nitrogen and 
oxygen. How many volumes of the products are formed? 

6. A compound has the composition C = 39.9, H = 6.7, O = 53-4, 
and the vapor density is 1.906. What is the molecular formula? 



CHAPTER XXVII 



FLUORINE — BROMINE — IODINE 

404. The halogen family. — Fluorine, bromine, and 
iodine, together with chlorine (see Chapter XI), constitute 
a family of related ele- 
ments often called the 
halogens. The elements 
and their analogous com- 
pounds have similar prop- 
erties, differing mainly in 
degree (400, 418). 

405. Occurrence of 
fluorine. — Fluorine is 
the most active of these 
elements, and is never 
found free in nature. It 
occurs abundantly in 
combination with cal- 
cium as calcium fluoride . , ^ n 

a ., Fig. 148. — Moissan (1852-1907) 

(fiuor spar, fluorite, 

CaF2) . Other native compounds are cryolite (NasAlFe) and 
apatite (Ca5F(P04)3). 

406. Preparation of fluorine. — Fluorine was first isolated in 18S6 
by the French chemist IMoissan (Fig. 148) by the electrolysis of hydro- 
fluoric acid in a solution of acid potassium fluoride (HKF>). The ex- 
periment was difficult and dangerous owing to the corrosive proper- 
ties of both acid and element. 

407. Properties of fluorine. — Fluorine is a greenish yellow gas, 
though lighter and more yellow than chlorine. Chemically, fluorine 

337 




338 PRACTICAL CHEMISTRY 

is intensely active. Most elements unite with it readily, the combin- 
ing being accompanied by much heat and light. The compounds 
formed are fluorides. It does not combine with oxygen or nitrogen, 
while some metals, e.g. gold, platinum, and copper, are not readily 
(or only slightly) attacked by it. 

408. Hydrogen fluoride is prepared by the interaction 
of concentrated sulphuric acid and calcium fluoride. The 
experiment is performed in a lead dish. The equation for 
the reaction is : — 



CaFo + H0SO4 ^ 


= H2F0 + 


CaS04 


Calcium Sulphuric 


Hydrogen 


Calcium 


Fluoride Acid 


Fluoride 


Sulphate 



Hydrogen fluoride is gas, which can be readily condensed 
to a colorless Uquid boihng at about 19° C. The gas forms 
fumes in moist air and dissolves readily in water. (Com- 
pare 155.) The solution is hydrofluoric acid. Hydrogen 
fluoride in the form of gas, hquid, or solution is a dangerous 
substance. The gas is extremely poisonous, and the 
hquid, if dropped on the skin, produces terrible sores. 
Owing to its corrosive properties, hydrofluoric acid is kept 
in hard rubber or wax bottles. 

Hydrofluoric acid behaves chemically like hydrochloric 
acid. Thus, it interacts with metals, forming fluorides, 
and it neutralizes bases, forming salts and water. Unlike 
hydrochloric acid, it forms both normal and acid fluorides, 
e.g. potassium fluoride (K2F0) and acid potassium fluoride 
(HKF2). 

409. Etching with hydrofluoric acid. — The acid and 
moist gas attack glass, and are used extensively in etching. 
Glass, as we have seen, is essentially a mixture of silicates 
and sihca (394). Hydrofluoric acid interacts with these 
compounds and forms among other substances a volatile 
compound called sihcon tetrafluoride (SiF4). Thus the 



FLUORINE — BROMINE — IODINE 339 

acid disintegrates the glass — literally ''eats" or etches 
it. Typical equations for the reactions in case of ordinary 
sodium glass are : — 

NaoSiOs + 3H0F0 = SiF4 -h Na,F, + 3H2O 

Sodium Hydrolluoric Silicon Sodium Water 

Silicate Acid Tetratluoride Fluoride 

CaSiOa + 3H0F2 = SiF4 + CaFo + 3H0O 
Calcium Hydrofluoric Silicon Calcium Water 

Silicate Acid Tetrafluoride Fluoride 

When hydrofluoric acid interacts with silicon dioxide, the 
equation for the reaction is : — 

Si02 + 2H.2F0 = SiF4 + H2O 

Silicon Dioxide Hydrofluoric Acid Silicon Tetrafluoride Water 

In etching with hydrofluoric acid, the glass is thinly coated with 
wax, and the design or marks to be etched are scratched through the 
wax. The glass is then exposed to the gas or liquid, which attacks the 
unprotected places. When the wax is removed, a permanent etching 
is left. Sometimes the design or marking is made more conspicuous 
by filling the etched cavity with an insoluble white 
or black substance. Hydrofluoric acid is utilized 
in marking the scales on thermometers, tubes, and 
other graduated glass instruments, and also in 
etching designs on glassware (Fig. 149). 




410. Occurrence and preparation of 
bromine. — Bromine is never found free, 
but bromides are widely distributed, espe- 
cially magnesium and sodium bromides. 
The salt springs and wells of Ohio, West p^g j^^ _ 
Virginia, Pennsylvania, and ^lichigan con- Etching on glass 
tain bromides ; large quantities are found tumbler. (De- 

r>. r . /Mne>\ signcd and exe- 

m the salt deposits at Stassfurt (462). ^^^^^ ^^^ j^j^j^ 

Bromine is prepared in the laboratory by school pupil) 



340 



PRACTICAL CHEMISTRY 



heating potassium bromide with manganese dioxide and 
sulphuric acid. If an apparatus Uke that shown in Fig. 
150 is used, part of the bromine vapor escapes and part 
condenses to a hquid, which collects in the U-bend. The 
complete equation for the reaction, which takes place in 
several stages, is : — 



2KBr + 2H2SO4 

Potassium Sulphuric 
Bromide Acid 



+ Mn02 = Bra + MnS04 + K2SO4 + 2H2O 
Manganese Bromine Manganese Potassium Water 

Oxide Sulphate Sulphate 



Another method consists in warming a bromide solution with chlo- 
rine water ; an equation for this method is : — 



MgBro + Clo 

Magnesium Bromide Chlorine 



Br2 + ^IgCb 

Bromine Magnesium Chloride 



Bromine is obtained industrially from the concentrated 
solution of bromides, called bittern, which is left after 
sodium chloride has been removed 
by crystallization from the brine of 
salt wells. Just enough chlorine is 
added to the solution to liberate the 
bromine ; steam is then introduced, 
and the bromine distills over. 

It is interesting to note that the French 
chemist Balard, who discovered bromine 
in 1826, obtained it from bittern. 




Fig. 150. — Apparatus for 
preparing bromine in 
the laboratory 



411. Properties of bromine. — 

Bromine is a reddish brown liquid 
which is about three times as heavy 
as water. It is a volatile hquid, boiling at about 59° C. 
The vapor has a disagreeable odor. This property sug- 
gested the name bromine (from a Greek word meaning 
stench). The vapor irritates the mucous membrane of 
the eyes, nose, and throat; a bottle of bromine should 



FLUORINE — BROMINE — IODINE 341 

not be opened unless it is in the hood. Bromine is some- 
what sohil^le in water. The solution, called bromine 
water, has a reddish brown color. Bromine dissolves in 
carbon disulphide and carbon tetrachloride ; the solution 
is reddish yellow. 

Liquid bromine burns the flesh frightfully, and care 
should be used in preparing or working with it. 

The chemical behavior of bromine is similar to that of 
chlorine, though bromine is less active. Thus, it com- 
bines with metals and other elements ; it also bleaches. 

412. Compounds of bromine are similar to those of chlorine. 
Hydrogen bromide (HBr) is a colorless, pungent gas, which fumes 
in the air and dissolves freely in water. This solution is called hydro- 
bromic acid ; it is much like hydrochloric acid. Bromides are salts 
of hydrobromic acid, though many are formed by direct combination 
with bromine. Potassium bromide (KBr) is a white solid, made by 
decomposing iron bromide with potassium carbonate ; it is used as a 
medicine. Silver bromide (AgBr) is used extensively in making 
photographic films and plates. 

413. Occurrence of iodine. — Iodine, like chlorine and 
bromine, is found in nature only in compounds. Tobacco, 
water cress, cod-liver oil, oysters, and sponges contain mi- 
nute quantities. Sea water contains a very small proportion 
of combined iodine. This is assimilated by certain sea- 
weeds. Much iodine was formerly extracted from the 
ash of certain seaweeds. The French chemist Courtois, 
who discovered iodine in 181 2, prepared it from seaweed. 

Iodine compounds, chiefly sodium iodate (NalOs), occur 
in the deposits of saltpeter (sodium nitrate) in Chile, and 
most of the iodine is now obtained from this source. 

414. Preparation of iodine. — Iodine is prepared in the 
laboratory by a method similar to that used for bromine. 
Potassium (or sodium) iodide, manganese dioxide, and 



342 PRACTICAL CHEMISTRY 

sulphuric acid are heated together. The iodine is evolved 
as a violet colored vapor. The equation is : — 

2KI + 2H2SO4 + Mn02 = I2 + MnS04 + K2SO4 + 2H2O 
Potassium Sulphuric Manganese Iodine Manganese Potassium Water 

Iodide Acid Dioxide Sulphate Sulphate 

Iodine is prepared in a commercial scale from crude Chile 
saltpeter. Sodium sulphites are added to the liquid left 
after sodium nitrate (NaNOs) has been removed by crystal- 
lization from a solution of the crude saltpeter, thus : — 

2NaI03 + 3NaoS03 + 2HNaS03 = I2 -r S^^^SO, + H2O 

Sodium Sodium Acid Sodium Iodine Sodium Water 

lodate Sulphite Sulphite Sulphate 

In extracting iodine from the seaweed, the ash is treated with 
sulphuric acid and manganese dioxide or with chlorine. 

415. Properties of iodine. — Iodine is a dark grayish crys- 
talline solid, which is nearly five times as heavy as water. 
It is volatile at ordinary temperatures, and when gently 
heated changes into a beautiful violet colored vapor, which 
readily solidifies on a cold surface, often in the upper part 
of the vessel in which the iodine is -heated. 

This property of iodine, viz. ready transformation from solid into 
vapor and back directly into solid, is utilized in purifying iodine. The 
crude substance is heated gently and the vapor condensed ; the non- 
volatile impurities remain behind. This process is called sublima- 
tion and is frequently used to purify substances (180). 

The striking color of the vapor suggested the name iodine 
(from a Greek word meaning violetlike), which was given 
to the element by the EngHsh chemist Davy, who studied 
the substance soon after its discovery. The vapor is nearly 
nine times as heavy as air, and has an odor resembhng 
dilute chlorine, though less irritating. Iodine melts at 
about 114* C. and boils at about 185° C. 



FLUORINE — BROMINE — IODINE 343 

Iodine dissolves slightly in water but freely in alcohol, 
chloroform, carbon disulphide, ether, or potassium iodide 
solution. The chloroform and carbon disulphide solutions 
are violet, but the others are brown, or even black. Iodine 
and its solutions turn the skin brown. 

Iodine turns cold starch solution blue. A minuie 
trace of iodine may thus be detected. The nature of this 
blue substance is unknown. The presence of starch in 
many vegetable substances can thus be shown (349). 

In chemical conduct iodine resembles chlorine and bromine, but 
iodine is less active. Bromine and chlorine displace iodine from 
many of its compounds. 

416. Uses of iodine. — A solution of iodine in alcohol 
(or in alcohol and potassium iodide), called tincture of 
iodine, or merely '' iodine," is applied to the skin to harden 
it, to prevent the spread of eruptions, or to reduce swellings. 
Iodine is used to make iodoform (CHI3), which is used as 
an antiseptic for wounds. Large quantities of iodine are 
made into iodides, drugs, and dyes. 

417. Compounds of iodine. — Hydrogen iodide and hydriodic 
acid (HI) are much like the corresponding compounds of chlorine and 
bromine, though unlike them in being reducing agents. Iodides 
are salts of hydriodic acid. In general behavior they are similar to 
bromides and chlorides. The best known salt is potassium iodide 
(KI). Silver iodide (Agl), like silver bromide, is used in photog- 
raphy. 

418. The halogen elements and the periodic classifi- 
cation. — The halogen elements illustrate typically the 
periodic classification. These elements, as arranged in 
the periodic table, increase in atomic weight from fluorine 
(19.0) through chlorine (3546) and bromine (79.92) to 
iodine (126.92), and many of their properties are graded 
in this order. Thus, as we pass from fluorine to iodine 



344 PRACTICAL CHEMISTRY 

the specific gravity increases, the color grows deeper, the 
volatiKty decreases, and the melting points of the solidi- 
fied elements increase. The intensity of the chemical 
action decreases as we pass from fluorine to iodine. 

EXERCISES 

1. Review topics: (a) Chlorine. (6) Compounds of fluorine and 
silicon, (c) Periodic classification of the elements. 

2. Summarize the chief properties of fluorine and hydrogen fluoride. 

3. Describe the process of etching glass. Write the equations. 

4. Write the equations for the preparation of (a) hydrogen fluoride, 
(b) bromine, (c) iodine, (d) silver bromide. Write (d) in ionic form. 

5. Questions for home study: (i) Why did Moissan use acid po- 
tassium fluoride in the electrolysis of hydrofluoric acid? (2) Hydri- 
odic acid and iodine compounds often turn dark on standing. Why? 
(3) What gas resembles bromine vapor in color? (4) How does 
bromine differ from all other elements previously studied (in this book)? 

(5) How would you identify by experiment (a) sand, (b) tincture of 
iodine, (c) calcium fluoride, ((/) potassium bromide, (e) silver iodide ? 

6. Compare fluorine, chlorine, bromine, and iodine. 

7. Essay topics: (a) Discovery of the halogen elements, (b) Iodine 
industry in Chile, (c) Etching with hydrofluoric acid, {d) Uses of 
iodine. 

PROBLEMS 

1. Calculate the per cent of fluorine in (a) hydrogen fluoride (H2F2), 

(6) silicon tetrafluoride, {c) apatite, (d) calcium fluoride. 

2. Calculate the per cent of bromine or iodine in (a) sodium bromide, 
(b) hydrogen bromide, (c) calcium iodide, (d) sodium iodate. 

3. How much (a) calcium sulphate and {b) hydrogen fluoride are 
formed by heating 60 gm. of fluor spar with sulphuric acid? 

4. How much iron iodide (Fcsls) can be made by the interaction of 
iron and 300 gm. of iodine ? 

5. How much potassium bromide (75 per cent pure) is necessary to 
prepare 47 gm. of bromine? 

6. How much potassium iodide (80 per cent pure) is necessary to 
prepare 47 gm. of iodine? 

7. Write the formulas of the fluoride, bromide, and iodide of Al, 
ammonium, Ba, Ca, copper (ous and ic), Fen, Fe™ Pb, magnesium, 
Sbni, Si, Hg (ous and ic), Snn, Sniv, zinc. 



FLUORINE — BROMINE — IODINE 345 

8. Calculate the atomic weight of (luorinc, bromine, or iodine from 
the following: (a) i gm. of CaFa gives 1.745 gm- of CaSO*; (b) 3.946 gm. 
of Ag (dissolved in HXO3) require 4-353 gm- oi KBr for precipita- 
tion; (c) 6.3835 gm. of silver iodide give 3-8965 gm- of silver chloride. 

9. Calculate the simplest formula corresponding to (a) F = 48-72, 
Ca = 51. 28; {b) Br = 67.22, K = 32.77; (c) I = 76.5, K = 23.49. 



CHAPTER XXVIII 



PHOSPHORUS — PHOSPHATES AND FERTILIZER — ARSENIC 
— ANTIMONY — BISMUTH 

419. Introduction. — ■ These elements together with ni- 
trogen belong to Group V of the periodic classification. 

420. Occurrence of phospho- 
rus. — Free phosphorus is not 
found in nature, but phosphates 
are numerous and abundant. 
The most common phosphate is 
calcium phosphate (Ca3(P04)2), 
which is the chief ingredient of 
'' phosphate rock " and bones ; 
about 80 per cent of bones is 
calcium phosphate. Small 
amounts of phosphates occur 
in fertile soils and some iron 
ores. Complex organic phos- 
phorus compounds are found 
in the germs of seeds and the nerves, brains, and muscles 
of animals. 

421. Phosphorus is manufactured from calcium phos- 
phate. — In the new process phosphorus is manufactured 
in an electric furnace (Fig. 151). The mixture of calcium 
phosphate, carbon, and sand is introduced at A and fed 
into the furnace by the screw B. An electric current passed 
between the electrodes EE produces the intense heat 
needed for the chemical change. The phosphorus vapor 

346 




Fig. 151. — ■ Electric furnace 
for the manufacture of phos- 
phorus 



PHOSPHORUS 347 

escapes through C into a condenser; the Uquicl residue, 
which is f^ssentially calcium siUcate, is drawn off as slag at 
D. The equation for the chemical change is : — 

2Ca3(P04)2 + 6Si0.2 + loC = r4 + loCO + 6CaSi03 

Calcium Sand Carbon Phosphorus Carbon Calcium 

Phosphate :Monoxidc Silicate 

In the older process (not used now to any extent) the finely ground 
material is heated with enough sulphuric acid to produce the following 
change : — 

Ca3(P04)2 + 3H.SO4 = 2H3PO4 + 3CaS04 

Calcium Sulphuric Phosphoric Acid Calcium 

Phosphate Acid (Ortho-) Sulphate 

The phosphoric acid is mixed with sawdust, coke, or charcoal, and 
dried, being changed thus : — 

H3PO4 = HPO3 + HoO 

Phosphoric Acid (Ortho-) Phosphoric Acid (Meta-) Water 

The dried mass is heated to a high temperature in clay retorts, the 
change being substantially : — 

4HPO3 + 12C = P4 + 2H0 + 12CO 

Phosphoric Acid (Meta-) Carbon Phosphorus Hydrogen Carbon Monoxide 

The phosphorus distils as a vapor through a pipe into a trough of 
water where it condenses to a heavy liquid. 

The phosphorus obtained by either process is purified, 
melted under water, and cast in molds into small sticks. 

422. Properties of phosphorus. — The phosphorus pre- 
pared by the methods just described is the white or ordi- 
nary form. It is a colorless, or sHghtly yellow, translucent 
solid. The color deepens by exposure to Kght. At ordi- 
nary temperatures it is soft like wax, and can be cut with 
a knife. At low temperatures it is brittle. It melts at 
44° C, but it should always be melted under water. When 
exposed to air it oxidizes quickly and gives off white fumes. 
At about 35° C. it takes fire and burns with a briUiant flame. 



348 PRACTICAL CHEMISTRY 

Since white phosphorus oxidizes so rapidly at lower 
temperatures, it is apt to take fire almost spontaneously. 
Hence it is kept beneath water and should not be handled 
unless it is wet ; indeed it is better not to touch it at all, but 
to use wet forceps when it is necessary to transfer it or to 
hold it while it is being cut under water. Moreover un- 
usual care should be taken not to leave bits of phosphorus 
in deflagrating spoons or lying about the laboratory. 

In moist air white phosphorus is slightly luminous, as 
may be easily seen by rubbing the head of a phosphorus- 
tipped match in a dark room. This property gave the 
element its name (from a Greek word meaning light 
bringer) . 

White phosphorus has a faint odor. It is very poison- 
ous, and the fumes cause a dreadful disease, which rots 
the bones, especially the jaw bones. It is practically in- 
soluble in water, but dissolves readily in carbon disulphide. 

423. Red phosphorus is made by heating white phos- 
phorus to 2 5o°-300° C. in a closed vessel freed from air. 
Red phosphorus is a reddish brown powder. It is opaque 
and odorless, does not glow in the air, nor does it ignite 
until heated to about 250° C. It is not poisonous, and 
does not dissolve in carbon disulphide. Its specific gravity 
varies from 2.1 to 2.3, that of the white form being 1.83. 
It does not combine with oxygen at ordinary tempera- 
tures and being less dangerous than yellow phosphorus can 
be handled safely. 

424. The formula of phosphorus. — The weight of 22.4 liters of 
each kind of phosphorus vapor (up to about 1500° C.) is approximately 
128 grams. Hence a molecule must contain four atoms, and the 
molecular formula of the vapor is P4 (207) . 

425. Matches. — On account of its ready inflamma- 
bihty phosphorus until recently was used in the manu- 



PHOSPHORUS 349 

facture of matches. Phosphorus sulphide (P4S3) is now 
used in the United States as a substitute for the element. 
This change was made on account of a prohibitive tax (two 
cents per hundred matches) upon phosphorus matches, 
levied mainly to protect the workmen from the disease 
caused by breathing phosphorus fumes. The sulphide is 
not poisonous and is as suitable for match heads as phos- 
phorus itself. 

Ordinary matches are made by dipping one end of the match 
sticks first into melted paraffin and then into the " phosphorus mix- 
ture." The latter consists usually of different proportions of phos- 
phorus sulphide, manganese dioxide or another oxidizing substance, 
and glue or some other binding material mixed with a little coloring 
matter. These matches are the ordinary friction kind. By rubbing 
them on a rough surface the friction generates enough heat to ignite 
the phosphorus compound, which continues to burn owing to the oxy- 
gen supplied (mainly) by the oxidizing agent, and the heat thereby 
produced sets fire to the paraffin, and this in turn kindles the wood. 

In safety matches the head is usually a colored mixture of antimony 
sulphide, potassium chlorate, and glue, while the surface on the box 
upon which the match must be rubbed to ignite is a mixture of red 
phosphorus, glue, and powdered glass. 

426. Phosphoric acid and phosphates. — When phos- 
phorus burns freely in air, a white, snowlike solid is formed 
called phosphorus pentoxide (PoOs)- It is very deliques- 
cent, quickly withdrawing moisture from air and com- 
bining vigorously with water with a hissing noise. It is 
often used in the laboratory to dry gases, being much more 
effective than calcium chloride and sulphuric acid, which 
are similarly employed (90). 

With hot water, phosphorus pentoxide forms phos- 
phoric acid, thus : — 

P2O5 + 3H2O = 2H3PO4 

Phosphorus Pento.xide Water Orthophosphoric Acid 



350 PRACTICAL CHEMISTRY 

Phosphorus pentoxide is therefore called phosphoric an- 
hydride. (Compare 262.) 

Phosphoric acid (sometimes called orthophosphoric 
acid) is tribasic and forms three series of salts (phosphates), 
depending on the number of hydrogen atoms replaced by 
a metal. Orthophosphates — usually called simply phos- 
phates — have several names based on the replacement of 
the hydrogen. Thus, Na3P04 is normal or trisodium phos- 
phate ; HNa2P04 is acid or disodium phosphate; and 
H2NaP04 is acid or monosodium phosphate. Disodium 
phosphate (HNa2P04) is the commercial " sodium phos- 
phate." Similarly, we have normal calcium phosphate 
(Ca3(P04)2), and acid calcium phosphates, e.g. H2Ca2(P04)2 
and H4Ca(P04)2. 

The '' acid phosphate " sold as a beverage is a solution of one or 
more acid calcium phosphates. In phosphate baking powder the 
acid is a calcium phosphate. 

With silver nitrate, phosphoric acid and soluble phos- 
phates precipitate yellowish silver phosphate (Ag3P04) ; 
they also precipitate yellow ammonium phosphomolyb- 
date from an excess of a nitric acid solution of ammonium 
molybdate. These reactions serve as tests for phosphoric 
acid and its salts. 

Phosphoric acid forms several kinds of ions besides hydrogen 

ions (H+), viz. H2PO4-, HPO4- ", and PO4 . It is a weaker acid 

than the common acids. 

427. Relation of phosphorus to life. — Phosphorus is 
essential to the growth of plants and animals. Plants 
take phosphates from the soil and store up the phosphorus 
compounds, especially in their seeds. Animals eat this 
vegetable matter, assimilate the phosphorus compounds, 
and deposit them in the bones, brain, and nerve tissue. 
Most of these phosphorus compounds are complex. Bones, 



PHOSPHORUS 



351 



however, as already stated, consist of about So per cent 
of calcium phosphate (Ca3(P04)2). 

The complex phosphorus compounds in the food con- 
sumed by animals are transformed by vital processes into 
phosphates which are eUminated to a large extent, and 
thus often find their way back into the soil. Here they 
are taken up again by plants, converted into complex com- 
pounds, stored up in the tissues and seeds, which are in 
turn eaten by animals. And so the process goes on — a 
phosphorus cycle analogous to the carbon cycle (29. 391 
(end), Fig. 17). 

428. Phosphate fertilizers. — In order to furnish plants 
with phosphorus, various phosphorus-bearing substances 
are added to the soil in the form of fertiHzers. 

Artificial fertilizers are made from phosphate rock. This 
occurs in large beds in North and South Carohna, Tennes- 
see, and Florida (Fig. 152). It consists of the hardened 




Courtesy American Agricultural Chemical Company 
Fig. 152. — Mining phosphate rock in Florida. The powerful stream 
of water washes the phosphate rock down into a pit from which both 
water and rock are pumped to washers, where sand is removed and 
low grade rock rejected. When dried, the phosphate rock is ready 
for manufacture into fertilizer 



352 PRACTICAL CHEMISTRY 

remains of land and marine animals, and is mainly trical- 
cium phosphate (Ca3(P04)2). It is insoluble in water, 
and must be changed into the soluble monocalcium salt 
(H4Ca(P04)2), so that it can be evenly distributed through 
the soil and easily taken up by plants. This soluble salt 
is called " superphosphate of lime." When phosphate 
rock is treated with sulphuric acid, the changes involved 
may be written thus : — 

Ca3(P04)2 + 2H2SO4 = H4Ca(P04)2 + 2CaS04 

Tricalcium " Superphosphate Calcium 

Phosphate of Lime " Sulphate 

Ca3(P04)2 + 3H2SO4 = 2H3PO4 + 3CaS04 

Phosphoric Acid 

Ca3(P04)2 + H2SO4 = HoCa2(P04)2 + CaS04 

Dicalcium Phosphate 

The mixture of superphosphate and calcium sulphate, 
when ground and dried, is ready for use as a phosphate 
fertilizer. Usually " superphosphate " is mixed with com- 
pounds of nitrogen (116) and of potassium (463, 469) to 
form a complete fertilizer. 

The law requires the dealer to state the analysis of the fertilizer 
on the bag or label. The per cent of phosphorus is usually stated as 
per cent of P2O5, which is popularly called " phosphoric acid " (426). 

The beneficial results of adding (complete) fertihzer to 
the soil are strikingly shown in Fig. 153. In the wheat 
field (top), the left was fertihzed and the right was unferti- 
lized ; the left yielded lyf bushels per acre but the right 
only 5. The contrast is more conspicuous in the sorghum 
field (bottom) where the unfertiHzed part (left) yielded 
only 66 gallons of sirup per acre, whereas the right yielded 
140. From the cotton field (middle) about 1350 pounds 
of seed cotton were obtained from the heavily fertilized 




Fig. .O.J. 



■ ci.^L v>l fertilized and unfertilizetl fields 



354 PRACTICAL CHEMISTRY 

part and about 700 pounds from the scantily fertilized 
part. 

429. Occurrence of arsenic. — Arsenic occurs combined 
with sulphur or a metal, or with both, e.g. as realgar (AS2S2), 
orpiment (AS2S3), arsenopyrite or mispickel (FeSAs). Many 
sulphide ores {e.g. copper ores) contain arsenic. 

430. Properties and uses of arsenic. — Arsenic is a britde, steel- 
gray solid having a metallic luster. Heated in the air. it volatilizes 
without melting, and the vapor has an odor like garlic. At about 
180° C. it burns in the air with a bluish flame, forming arsenious 
oxide (AS2O3). Arsenic is used to harden the lead made into 
shot. 

The molecules of arsenic vapor at about 650° C. contain four atoms, 
hence the molecular formula As4. (Compare 424.) 

431. Arsenic trioxide (AS2O3) is the most important com- 
pound of arsenic. It is often called '' white arsenic," 
or simply " arsenic." It is obtained as a by-product in 
roasting ores that contain arsenic. It is odorless, has a 
slight taste, and dissolves slightly in cold water. 

It is converted readily by hot hydrochloric acid into 
soluble arsenic trichloride (AsCls), which is a convenient 
solution to use in the laboratory. 

Arsenic trioxide is used to a limited extent in making 
pigments for green paints, as the poisonous ingredient of 
fly and rat poison, in the manufacture of glass (especially 
plate glass), in making arsenic compounds {e.g. insecticides 
(432)), for destroying weeds, and in preserving skins in 
museums. 

Arsenic trioxide is an active poison. The antidote for 
arsenic poisoning is fresh ferric hydroxide, which is made by 
adding ammonium hydroxide to a ferric salt, e.g. ferric 
chloride, which forms an insoluble substance with the ar- 
senic compound. 



ARSENIC 355 

432. Other arsenic compounds. — The native mineral orpiment 
(As-jSa) is used in making a yellow paint, and realgar (AsjSj) a rrd 
paint. Paris green (CuaCAsOOL'-CuCCzHaOj)-..) and lead arsenate 
(Pb3(As04)2) are effective insecticides and are used extensively to e.\- 
terminatc potato bugs and other insect pests. 

433. Test for arsenic. — The formation of yellow arsenious sul- 
phide (As-jSs) by passing hydrogen sulphide into an arsenic solution 
containing hydrochloric acid is the usual test for arsenic. 

434. Occurrence and preparation of antimony. — Small 
quantities of free antimony are found. The most common 
native compound is the sulphide (stibnite, SboSa). 

Antimony is prepared by roasting the sulphide and reducing the 
oxide with charcoal, thus : — 

Sb.Ss + 5O2 = SboO.; + 3SO, 

•\ntimony Sulphide Antimony Oxide Sulphur Dio.xide 

SboOi + 4C = 2Sb + 4CO 
In another method the sulphide is heated with iron, thus : — 
Sb,S, + 3FC = 2Sb -f 3FcS 

Antimony Sulphide Antimony Iron Sulphide 

435. Properties of antimony. — Antimony is a silver- 
white, crystalline, brittle solid. It melts at about 630° C. 
At ordinary temperatures it does not tarnish in the air, 
but when heated it burns with a bluish flame, forming 
white, powdery antimony trioxide (Sb203). Nitric acid 
oxidizes it to antimonic acid (H3Sb04) and aqua regia trans- 
forms it into soluble antimony trichloride, which is a con- 
venient solution of antimony for use in the laboratory. 

436. Antimony is used to make certain alloys. When 
antimony is melted with some metals, especially lead and 
tin, the metals dissolve one another. Such a metallic 
solution upon solidifying forms an alloy. Alloys have 
different, often very different, properties from the original 



356 PRACTICAL CHEMISTRY 

metals. Thus, an alloy of lead (70 to 80 per cent), anti- 
mony, and tin expands on cooling and is harder than lead. 
It is used as type metal because it makes the face of the 
type hard and reproduces sharply the dots and fme lines 
(of the mold). Babbitt metal contains antimony, tin, and 
copper. It is used for the bearings of machines to reduce 
friction. Other anti-friction alloys contain lead, tin, anti- 
mony, and a little copper. Another alloy containing an 
appreciable proportion of antimony is Britannia metal, 
which is used in making ornaments and tableware. 

437. Compounds of antimony. — Antimony forms stibine (SbHa), 
which is analogous to ammonia (NH3) , and to arsine (AsHs) . It also 
forms complex compounds in which the group SbO — called anti- 
monyl — acts as a univalent radical, e.g. tartar emetic or potassium 
antimonyl tartrate (KSbOC4H406), which is used as a medicine and 
as a mordant in dyeing cotton. Antimony trisulphide (SboSs) is ob- 
tained as an orange red precipitate by passing hydrogen sulphide gas 
into a solution of an antimony salt — the usual test for antimony. 
This sulphide is used in making the red rubber tubing and stoppers 
used in the laboratory. Antimony trichloride (SbCls) is formed by 
interaction of the metal and aqua regia. It hydrolizes readily, 
i.e. interacts with water, thus : — 

SbCls + HoO = SbOCl + I-ICl 

Antimony Trichloride Water Antimony Oxychloride Hydrochloric Acid 

Antimony oxychloride is a white solid insoluble in water, and its 
formation is sometimes used as a test for antimony. 

438. Occurrence and preparation of bismuth. — Bis- 
muth is found in the native state, though it is not abundant 
nor widely distributed. The oxide (bismite, Bi^Oa) and 
the sulphide (bismuthinite, Bi2S3) are native compounds. 

439. Bismuth is prepared from the native metal by melting it on 
an inclined plate and allowing it to drain away from the solid impu- 
rities. Sometimes the sulphide is roasted, and the resulting oxide is 
reduced with charcoal, as in the case of antimony. 



ANTIMONY 



357 



440. Properties of bismuth. Hismuth is ii silvery 
metal with a reddish tinge. Like iintimony, it is very 
brittle. When heated in air it burns with a bluish flame, 
forming the yellowish trioxidc (Bi203). Hydrochloric acid 
does not readily attack it, but hot concentrated nitric acid 
converts it into a nitrate and hot sulphuric into a sulphate. 
With aqua rcgia it forms bismuth chloride (BiCls). 

441. Bismuth is used in making alloys which have very 
low melting points. The metal itself melts at 269° C. But 
alloys of bismuth, lead, 
and tin melt at a much 
lower temperature. For 
example, Newton's metal 
melts at 94.5° C. and 
Rose's metal at 93.8° C. ; 
while Wood's metal, 
which contains the metal 
cadmium also, melts at 
only 60.5^ C. 

These alloys are called 
fusible metals. They 
are used in making 
safety plugs for steam 
boilers, fuses for elec- 
trical apparatus, and as 
connecting Hnks to hold 
in place automatic fire- 
proof doors and to close 
the heads in the automatic 
quently installed in 
metal at A). 

In case of fire, the heat soon melts the fusible metal in 
the sprinkler heads, thereby providing openings in the 




[g. 154. — Sprinkler head, fusible 
link, and fireproof door (held in place 
by a link of fusible metal). Fusible 
metal is at A 

sprinkling apparatus fre- 
large buildings (Fig. 154 — fusible 



358 PRACTICAL CHEMISTRY 

pipes from which the water flows. The fireproof door is 
kept open by a weight until the heat melts the fusible metal 
and lets the door dose automatically. (Study Fig. 154.) 

442. Compounds of bismuth. — Bismuth sulphide (Bi-iSs) is ob- 
tained as a black precipitate by passing hydrogen sulphide into a solu- 
tion of a bismuth salt. The trichloride (BiCls) is formed by treating 
bismuth with aqua regia. With an excess of water the trichloride 
undergoes hydrolysis, forming basic bismuth chloride (Bi(0H)2Cl), 
which by loss of water becomes bismuth oxychloride (BiOCl). The 
latter is a pearl-white powder, insoluble in water, and its formation 
is the usual test for bismuth. 

EXERCISES 

1. Prepare a summary of phosphorus. 

2. Describe the manufacture of phosphorus (a) from a phosphate 
and sulphuric acid and (6) by the electrothermic method. 

3. Summarize the properties of (a) white phosphorus and (6) red 
phosphorus. Why is phosphorus so named? 

4. What is the formula of {a) tricalcium phosphate, (6) "sodium 
phosphate," (c) monohydrogen calcium phosphate, {d) superphosphate 
of lime, {e) dihydrogen dicalcium phosphate? 

5. Discuss the relation of phosphorus to Hfe. Compare with 
nitrogen and carbon in this respect. 

6. Describe the manufacture of phosphate fertilizer. 

7. Suggest an experiment to show that bones contain calcium phos- 
phate. 

8. By what other names is arsenic trioxide known? What is the 
antidote for arsenic poisoning? 

9. Describe a test for (a) arsenic, {h) antimony, and (c) bismuth. 

10. State the uses of alloys of (a) antimony and (h) bismuth. 

11. Topics for home study: (a) Fertilizers, {b) Matches, 
(c) Why does the soil need fertilizer? {d) Fireproof doors, 
(g) Sprinkler systems. (/) The nitrogen family and the periodic 
system. 

PROBLEMS 

1. Calculate the weight of phosphorus in 40 tons of calcium phos- 
phate. 

2. Calculate the percentage composition of (a) arsenic trioxide 
and arsenic pentoxide, and {h) antimony trichloride and antimony 



BISMUTH 359 

pentachloriflc. Show that these two sets of substances illustrate the 
law of multiple proportions. (Use exact atomic weights.) 

3. How many liters of air (containing 21 per cent of oxygen by 
volume) will be required to burn 5 gm. of phosphorus (standard 
conditions) ? 

4. How many gm. of phosphorus can be made by the electro- 
thermal process from a ton of calcium phosphate (70 per cent pure)? 

5. How much " superphosphate " can be made from 2 tons of 
phosphate rock (75 per cent calcium phosphate)? 



CHAPTER XXIX 



SODIUM AND ITS COMPOUNDS — POTASSIUM 

443. Metals. — The elements studied so far belong 
(with one or two exceptions) to the class of non-metals. 

Metals, e.g. sodium and 
calcium, have been dis- 
cussed, and the prop- 
erties of many com- 
pounds of metals have 
been quite fully treated, 
especially bases and salts. 
A table of the common 
metals and non-metals 
is given in 397. 

Sodium and potassium 
belong to a natural 
family of elements known 
as the alkali metals (399). 
444. Sodium is manu- 
factured on a large scale 
by the electrolysis of 
fused sodium hydroxide. This was the method by which 
the English chemist Davy isolated sodium in 1807 (Fig. 
155). Figure 156 is a sketch of one form of apparatus 
used at Niagara Falls, where many electrical industries 
are located. 

The body of the steel cylinder (5) rests within a heated flue. The 
cathode (C) is iron and the connected carbon rods (A A) constitute 

360 




Fig. 155. — Davy (1778-1829) 



SODIUM AND ITS COMPOUNDS 



361 



the anode. The sodium hydroxide in 
the neck (B) is soHd, but is kept 
melted in the main part. The melted 
sodium hydroxide conducts a current 
just as a solution does. As the elec- 
trolysis proceeds, sodium and hydrogen 
are liberated at the cathode, rise, and 
collect in the cylindrical pot (P). 
The hydrogen escapes to some ex- 
tent through the cover, but enough 
always remains in the upper part of P 
to protect the sodium from the air. 
The molten sodium, which floats on the 
top of the fused sodium hydroxide, is 
ladled out at intervals. Oxygen is 
liberated at the anode and escapes 
through the pipe without coming 
in contact with the sodium or hydro- 
gen. 




Fig. 156. — Sketch of the 
apparatus for the manufac- 
ture of sodium by the elec- 
trolysis of sodium hydrox- 
ide 



445. Properties of sodium. — 

Sodium is a silver- white metal. It is so soft that it can 
be easily molded with the fingers and cut with a knife. 
It floats on water, since its specific gravity is only about 
0.97. (Compare 396, 397.) 

446. Chemical conduct of sodium. — Heated in air^ 
sodium melts at 96° C, and at a higher temperature it 
volatilizes and burns with a brilHant yellow flame, forming 
sodium peroxide (NaoQo). This intense yellow color is 
characteristic of sodium and its compounds and is the usual 
test for sodium (free or combined). 

In moist air the bright surface of sodium quickly 
tarnishes, and the metal as usually seen has a yellow or 
brownish coating (instead of a shiny surface). It is, there- 
fore, kept under kerosene or a liquid free from water. 

Sodium decomposes water at ordinary temperatures, 
forming hydrogen and sodium hydroxide, thus : — 



362 PRACTICAL CHEMISTRY 

2Na + 2H2O = 2NaOH + Ho 

Sodium Water Sodium Hydroxide Hydrogen 

If held in one place upon the water by filter paper, enough 
heat is generated to set fire to the hydrogen, which burns 
with a yellow flame, owing to the presence of volatihzed 
sodium (49, 51). It combines vigorously with many non- 
metals, especially oxygen and chlorine. 

447. Sodium chloride (NaCl) is the most important 
compound of sodium. It is familiar under the name of salt 
or common salt. The presence of salt in the ocean, in 
lakes and springs, and in the earth is mentioned in the oldest 
historical records. It is one of the most abundant sub- 
stances, and is the chief of sodium compounds. 

448. Preparation of common salt. — Salt is obtained from sea 
water, rock salt deposits, and brines. Sea water contains nearly 
4 per cent of salts, and three fourths of this amount is sodium chloride. 
The water is evaporated, often by exposure to the sun, and the salt 
separates from the concentrated solution. Deposits of salt are found 
in many parts of the globe, the most important being in England, 
Austria-Hungary, and Germany. In these regions and some parts of 
the United States most of the salt is obtained from natural or arti- 
ficial brines. These solutions of salt are evaporated in shallow basins 
by the sun's heat or in large kettles. 

According to the standard established by the United States De- 
partment of Agriculture, dry table or dairy salt must not contain 
over 1.4 per cent of calcium sulphate, 0.5 per cent of calcium or mag- 
nesium chloride, and o.i per cent of matter insoluble in water. The 
dampness of salt is due to traces of magnesium and calcium chlorides 
which absorb moisture from the air (85). Pure salt does not absorb 
moisture. 

449. Properties and uses of salt. — Salt is rather uni- 
formly soluble in water, 100 gm. of water dissolving about 
36 gm. of salt at 20° C, and about 39 gm. at 100° C. 
(Fig. 43). It crystallizes in cubeSj and does not contain 



SODIUM AND ITS COMPOUNDS 363 

water of crystallization. The crystals, when heated, often 
snap open sharply {i.e. decrepitate), owin^ to the sudden 
evaporation of inclosed water. It melts at about 800'^ C. 

Salt is an essential ingredient of the food of man and 
animals. Besides its universal domestic use, enormous 
quantities are used in making sodium carbonate, sodium 
hydroxide, and hydrochloric acid. 

450. Sodium carbonate (Xa2C03) is next to sodium 
chloride in importance. Formerly it was obtained from 
the ashes of marine plants, hence the old name soda ash ; 
sodium chloride is now the source. The manufacture of 
sodium carbonate is one of the largest chemical industries. 
Two processes are used, the Solvay and the Leblanc. 

The Solvay process, which is operated very successfully in the 
United States, consists in saturating a cold concentrated solution of 
sodium chloride first with ammonia (gas) and then with carbon diox- 
ide. The equation for the complete chemical change is : — 

HoO + XaCl + NH3 + COo = HNaC03 -f XH4CI 

Water Sodium Ammonia Carbon Acid Sodium Ammonium 

Chloride Dioxide Carbonate Chloride 

The acid sodium carbonate is sparingly soluble in cold ammonium 
chloride solution, and is precipitated. The acid sodium carbonate 
is changed into normal sodium carbonate by heating, thus : — 

2HNaC03 = NaoCOs + COo + H,0 

Acid Sodium Sodium Carbon Water 

Carbonate Carbonate Dioxide 

The Leblanc process, which is the older and is used chiefly in 

Europe involves three reactions, (i) Sodium chloride is changed 
into sodium sulphate, thus : — 

2NaCl 4- H,SO, = NaoS04 + 2HCI 

Sodium Sulphuric Sodium Hydrochloric 

Chloride Acid Sulphate Acid 

(2) and (3) The sodium sulphate is changed into sodium carbon- 
ate by heating it with coal and calcium carbonate ; the two main 



364 



PRACTICAL CHEMISTRY 



changes, which are accomphshed by one operation, are represented 
thus : — 



Na2S04 


+ 2C = 


NaoS 


+ 


2CO2 


Sodium 
Sulphate 


Carbon 


Sodium 
Sulphide 




Carbon 
Dioxide 


NaoS + 


CaCOr. 


NaoCOa 




-}- CaS 


Sodium 
Sulphide 


Calcium 
Carbonate 


Sodium 
Carbonate 




Calcium 
Sulphide 



From the dark mass, called black ash, the sodium carbonate is dis- 
solved, and the solution evaporated to crystallization. 

451. Properties and uses of sodium carbonate. — Crys- 
tallized sodium carbonate (NaoCOs-ioH-zO) is often called 
sal soda or washing soda. It efHoresces, i.e. slowly loses 
its water of crystallization when exposed to air (84) . When 
heated, it iirst dissolves in its water of crystallization, and 
finally changes into the white anhydrous salt (Na2C03) 
which is called soda ash or calcined soda. 

It is soluble in water, and forms an alkaline solution 
which is widely used as a cleansing agent ; hence the name 
washing soda. Besides its use as a cleansing agent, 
enormous quantities are consumed in the manufacture of 
glass, soap, sodium hydroxide (456, first paragraph), and 
many other useful substances. 

452. Hydrolysis of sodium carbonate. — The alkalinity of sodium 
carbonate is due to h^^drolysis and can be explained in terms of the 
ionic hypothesis. Hitherto water has been called a non-electrolyte, 
i.e. it does not ionize. As a matter of fact it does form the ions H+ 
and 0H-, but to such a very slight extent that they have little of no 
effect in most cases. Under certain conditions, however, these ions 
participate in reactions, e.g. with sodium carbonate. 

Sodium carbonate ionizes into 2Na+ and CO3- ", but the unstable 
CO3 ions form HCO3 ions with the H ions from the slightly dis- 
sociated water. This removal of H ions finally leaves in the solu- 



SODIUM AND ITS COMPOUNDS ^65 

tion sufficient Oil ions to i)ro(lucc an alkaline reaction. Equations 
for these ionic reactions arc : — 

H2O = H+ + OH- 
NazCOs = 2Na+ + CO3- " 
2H- + CO3- - = H2CO3 

We may define hydrolysis as a chemical change in which water is 
a factor. A more restricted definition is the interaction of the ions 
of water with the ions of a dissolved salt. Salts of weak acids 
{e.g. H2CO3) and strong bases {e.g. NaOH) give alkaline solutions. 
On the other hand, salts of strong acids {e.g. HCl, H2SO4) and weak 
bases {e.g. Cu(0H)2, Fe(0H)3) give acid solutions. Salts of strong 
acids and strong bases give neutral solutions, e.g. NaCl, KX03,Xa2S04. 

453. Sodium bicarbonate (HXaCOs) is prepared by 
the Solvay process (see above), or by treating sodium car- 
bonate solution with carbon dioxide. 

It is a white powder, less soluble in water than the normal 
sodium carbonate. When heated alone or when mixed 
with an acid or an acid salt, sodium bicarbonate gives up 
carbon dioxide. This property early led to its use in cook- 
ing, and gave the names cooking soda, baking soda, or 
simply soda. 

Sodium bicarbonate is sometimes called acid sodium carbonate 
(though it is nearly neutral to litmus) and hydrogen sodium car- 
bonate. The neutral reaction of a solution of sodium bicarbonate 
is due to the fact that neither of its ions (Na+ and HCOs") affects 
Htmus. It should be noted that the name " acid " sodium carbonate 
emphasizes the method of formation (from carbonic acid) not the 
properties of the salt (292. 293). 

454. Baking powders. — Sodium bicarbonate is an es- 
sential ingredient of baking powders and of the various 
mixtures (except yeast) used to raise bread, cake, and other 
food. The other ingredient is a substance which has a 
weak acid reaction, such as acid calcium phosphate (426), 



366 PRACTICAL CHEMISTRY 

cream of tartar (acid potassium tartrate (HKC4H4O6)), 

or alum. 

If baking powder is mixed with water, carbon dioxide is slowly 
liberated. When pastry is raised with baking powder, or with a mix- 
ture of baking soda and cream of tartar, the escaping carbon dioxide 
puffs up the dough. Hence baking soda is often called saleratus — 
the salt that aerates (from the Latin words sal, salt, and aer, air). 

455. Sodium hydroxide or caustic soda (NaOH) is a 
white, crystalline, brittle, corrosive solid. It absorbs water 
(85) and carbon dioxide rapidly from the air, and is thereby 
changed into sodium carbonate. It dissolves readily in 
water, with rise of temperature. The solution is strongly 
alkahne and disintegrates many substances; hence the 
term caustic. It is a strong base and its solution contains 
a high per cent of hydroxyl ions (247). It melts easily. 

Immense quantities are used in making soap, paper pulp, 
phenol (CeHoOH), and dyestufTs, and in refining petroleum. 

456. Manufacture of sodium hydroxide. — The chem- 
ical process consists in boihng a dilute solution of sodium 
carbonate with calcium hydroxide; the main change is 
represented thus : — 

Ca(0H)2 + Na2C03 = 2XaOH + CaCOs 

Calcium Sodium Sodium Calcium 

Hydroxide Carbonate Hydroxide Carbonate 

The solution of sodium hydroxide is filtered from the 
insoluble calcium carbonate, evaporated, and the molten 
mass allowed to soUdify in small cyhndrical molds about 
the diameter of a lead pencil or in large iron barrels called 
drums; some is made into flakes. 

In the electrolytic process, which is operated on a large 
scale at Niagara Falls, and elsewhere, a solution of sodium 
chloride is used. When an electric current is passed 
through such a solution, sodium hydroxide and hydrogen 



SODIUM AND ITS COMPOUNDS 



;67 




Fig. 157. — The cell room of a plant for making sodium hydroxide by 

electrolysis 

are produced at the cathode and chlorine at the anode. 
The cells are constructed to prevent secondary action be- 
tween the sodium hydroxide and chlorine. A view of the 
cell room in an electrolytic alkali plant is shown in Fig. 157. 
The porous diaphragm type of cell is now largely used. 



An example of the porous 
diaphragm type is shown in Fig. 
158. The liquid can penetrate the 
porous diaphragm. Hence the 
diaphragm does not interfere with 
the flow of the electric current, but it 
does prevent the mixing of the two 
solutions. The diaphragm is a 
sheet of asbestos (mixed with iron 
oxide), which is supported on the 
perforated iron cathode. The graph- 
ite anode dips into the sotlium chlo- 
ride solution in the middle compart- 
ment ; here the solution is kept at 
a certain level by regulation of the 
inflow. The outer compartment 
contains kerosene. 




Fig. 158. — Sketch of the 
diaphragm type of appara- 
tus for the manufacture of 
sodium hydro.xide by the 
electrolysis of sodium chlo- 
ride solution 



3^^ 



PRACTICAL CHEMISTRY 



When the current is passing, the sodium ions (Na+) migrate to 
the cathode, lose their charges and become sodium atoms (Na), 
which interact with the water and form sodium hydroxide and 
hydrogen. The sodium hydroxide drops through the kerosene to 
the bottom of the outer compartment, and is drawn off through C ; 
the hydrogen escapes through B. Similarly, chlorine ions (Cl^) 
migrate to the anode, lose their charges, and become chlorine 
atoms (CI) which unite and escape as chlorine gas (CI2) through 
A. The equations may be written thus: — 

NaC] = Na+ + Cl" 
2Na+ = 2Na and 2C1~ = CI2 
2Na + 2H2O = 2NaOH + H2 

In the non-diaphragm cells the solutions are kept apart 
by partitions which extend nearly to the bottom of the 
cell and dip into a layer of mercury. 




Fig. 159. — Sketch of the non-diaphragm type of apparatus for the 
manufacture of sodium hydroxide by electrolysis of sodium chlo- 
ride solution 

An example of this type is shown in Fig. 159. The cell is a slate 
box divided into one cathode and two anode compartments. The 
T-shaped anodes (.4, A) of graphite and the cathode (C) of iron 
reach nearly to the mercury (shown in black). The anode compart- 
ments contain sodium chloride solution, while the cathode compart- 
ment contains sodium hydroxide solution; sodium chloride of the 
right concentration flows slowly and continuously into the anode 
compartments by means of the pipes E, E. 

During the electrolysis the chlorine ions (Cl~) ultimately become 
chlorine gas (CI2) and escape through the pipes D, D. The sodium 
ions (Na+) move toward the cathode, meet the mercury, are liberated 



SODIUM AND ITS COMPOUNDS 369 

on this intermediate cathode in the anode compartments and form 
an amalgam with it. When in operation the cell is slowly rocked on 
the device X, X and the sodium amalgam, but )iot the solutions, flows 
beneath the partitions from the anode compartments into the cathode 
compartment and back again. Once in the cathode compartment, 
the sodium is liberated at the cathode, and reacts with the water, 
forming hydrogen (Hj) and sodium hydroxide. The hydrogen es- 
capes through the pipe^. The sodium hydroxide solution is drawn 
off (through G) and replaced by water (through F). 

The sodium hydroxide solution is treated as described 
above (second paragraph, this section). The chlorine is 
stored or compressed. into steel cylinders (Figs. 35, 63). In 
some industries, e.g. paper pulp plants, both sodium 
hydroxide and chlorine are used. In that case, the chlo- 
rine is made into bleaching mixtures. 

457. Sodium sulphate (Na2S04) is a white solid. It dissolves 
readily in water, and when a strong solution made at 30° C. is cooled, 
large transparent, bitter crystals separate (Na2S04.ioH20), called 
Glauber's salt. Large quantities are obtained as a by-product in 
making hydrochloric acid (154). It is used in the glass and other 
industries. 

458. Sodium tetraborate or borax (Na2B407) is made 
from calcium borate (colemanite, Ca2B60ii.5H20) by boiling 
it with sodium carbonate and separating the borax by 
crystallization. The equation for the reaction is : — 

2Ca2B60u + 4Na2C03 + H2O = 3Na2B40- + 4CaC03 + 2NaOH 
Calcium Sodium Water Borax Calcium Sodium 

Borate Carbonate Carbonate Hydroxide 

Borax is a white crystalline sohd, having five or ten mole- 
cules of water of crystallization ; a common household 
form is the powdered crystals. The crystals readily 
effloresce and crumble in the air. When heated, crystal- 
lized borax loses its water of crystallization and swells into 
a white porous mass, which finally melts into a glass-like 



370 PRACTICAL CHEMISTRY 

solid. This glassy borax dissolves metallic oxides and is 
colored by them. 

If borax is melted on the end of a looped wire, the transparent 
globule is called a borax bead. These beads usually assume different 
colors after being heated in an oxidizing or a reducing flame, and 
the colors are characteristic of the metals (Fig. i6o). Thus, a copper 





Fig. i6cx — Testing with a borax bead in the oxidizing flame (left) and 
reducing flame (right) 

bead is made blue-green by an oxidizing flame and red by a reducing 
flame. Borax beads are used in testing small quantities of minerals. 

Borax is chiefly used in the manufacture of enamels for 
coating iron ware. The so-called '' granite " or " agate " 
ware and '' porcelain-lined " vessels are made of iron coated 
with an easily fused glass called enamel. Some is used 
for preserving meat, fish, cheese, and other foods, because 
it prevents the growth of certain bacteria. 

A solution of borax has a slight alkaline reaction owing to hydroly- 
sis (452) ; hence it is sometimes used instead of soap as a cleansing 
agent. Some soaps contain borax. 

Its power to dissolve oxides adapts borax for use in sol- 
dering and welding metals. Solder adheres only to clean 
metals, so a httle borax is used to dissolve the film of oxide 
on the surfaces to be joined. Considerable is consumed as 
an ingredient of ointments, lotions, and toilet powders. 

459. Sodium nitrate (NaNOs) is found abundantly in 
Chile and is often called Chile saltpeter. It is a white or 



SODIUM AND ITS COMPOUNDS 371 

brownish solid, which becomes moist in the air. Larjije 
quantities are used as a fertilizer, either alone or mixed 
with compounds of potassium and of phosphorus (428, 
and compare 116). It is used in making nitric (184) and 
sulphuric acids, and potassium nitrate. 

The deposits of sodium nitrate are in a dry region near the coast 
and cover a large area. Chile controls the industry and exports 
annually over a million tons. The crude salt, which is called caliche, 
looks like rock salt. The commercial salt is extracted from caliche 
by treating with water, settling, and evaporating the solution of the 
nitrate to crystallization. The final mother liquor is a source of 
iodine (413. 414). 

460. Sodium peroxide (Na-jO-j) is a yellowish solid. It is used 
to bleach straw and delicate fabrics. With water it liberates oxygen, 
thus : — 

2Xao02 + 2H2O =02 + 4XaOH 

Sodium Dioxide Water Oxygen Sodium Hydroxide 

461. Other sodium compounds. — Sodium cyanide (NaCN) is a 
white, deliquescent solid. It forms an alkaline solution (by hydroly- 
sis — 452). It is used in gold and silver plating and in the cyanide 
process of extracting gold. This compound is the sodium salt of 
hydrocyanic, or prussic, acid (HCN). It is a violent poison and great 
care must be taken in working with it. Sodium phosphate (426), 
sodium thiosulphate (276), acid sodium sulphite (263), and sodium 
siHcate (387) have been described. 

462. Potassium. — Potassium and its compounds are 
much like sodium and the corresponding compounds. Min- 
erals and many rocks contain potassium compounds. The 
minerals mica and feldspar are silicates containing potas- 
sium. By the decay of these, soluble potassium compounds 
find their way into the soil and are taken up by plants. 

Potassium salts are found in wood ashes and in the de- 
posits in wine casks. Sea water and mineral waters con- 
tain potassium salts, particularly potassium chloride and 



372 PRACTICAL CHEMISTRY 

potassium sulphate. Extensive beds of potassium salts 
are found in Germany, especially at Stassfurt. 

The most important Stassfurt potassium minerals are : — 

Sylvite — KCl CarnalHte — KCl, IMgCl2.6H20 

Kainite — KCl, MgS04.3H20 Picromerite — K2SO4, IVlgS04.6H20 

Potassium is prepared from potassium hydroxide by electroysis. 

Potassium is a soft, silver-white metal with a bluish tinge. 
It floats on water, the specific gravity being about 0.86. Its brilliant 
luster soon disappears in air, owing to rapid oxidation. Potassium 
as ordinarily seen is, therefore, covered with a grayish coating, and, 
like sodium, must be kept under mineral oil. It melts at 62.5° C, 
and at a higher temperature burns with a violet-colored flame. This 
color is characteristic of burning potassium, and is a test for the metal 
and its compounds. It is more active chemically than sodium. 

463. Potassium chloride (KCl) resembles sodium chlo- 
ride, and is used chiefly to prepare other potassium salts 
and as an ingredient of fertilizers (428). 

464. Potassium nitrate (KNO3), also called niter and 
saltpeter, is formed in the soil of many warm countries by 
the decomposition of nitrogenous organic matter. 

It is manufactured by mixing hot, concentrated solutions of sodium 
nitrate and potassium chloride. The equation for the reaction is : — 

NaN03 + KCl = KNO3 + NaCl 

Sodium Nitrate Potassium Chloride Potassium Nitrate Sodium Chloride 

The sodium chloride, being much less soluble than the potassium ni- 
trate, separates and is removed by filtration. By evaporating the 
filtrate, crystals of potassium nitrate separate and are further purified 
by recrystallization. The solubihty of these salts is shown in Fig. 43. 

Potassium nitrate melts at 2>33° C., and on further 
heating changes into potassium nitrite (KNO2) and oxygen. 
At a high temperature, potassium nitrate gives up oxygen 
readily, especially to charcoal, sulphur, and organic matter. 



SODIUM AND ITS COMPOUNDS 373 

This oxidizintj; power leads to its extensive use in making 
gunpowder, fireworks, matches, explosives, and in many 
chemical operations. 

Gunpowder is a mixture of potassium nitrate, charcoal, and sul- 
phur. The proportions differ with the use of the powder. A common 
variety contains 75 per cent of potassium nitrate, 15 of charcoal, and 
10 of sulphur. When gunpowder burns in a closed space, hot gases 
are suddenly formed. The pressure exerted by these gases forces 
the bullet from a gun and tears rocks to pieces. The chemical changes 
attending the explosion of gunpowder in a closed space are complex. 

465. Potassium chlorate (KCIO3) is used to prepare oxygen, and 
in the manufacture of matches and fireworks. It is manufactured 
by the electrolysis of potassium chloride in a special apparatus which 
allows the two products — chlorine and potassium hydroxide — to 
mix and interact. The equation for the reaction is : — 



3CI, + 6K0H = 


= KCIO3 + 5KCI + 


3H,0 


Chlorine Potassium 


Potassium Potassium 


Water 


Hydroxide 


Chlorate Chloride 





466. Potassium carbonate (K2CO3) is very soluble in 
water, and the solution, like that of sodium carbonate, has 
a strong alkahne reaction owning to hydrolysis (452). 

It was formerly obtained by treating wood ashes with water and 
evaporating the solution to dryness. The crude salt thus obtained 
has long been called potash, and a purer product is known as pearlash. 
The name of the element was suggested by the word potash; the 
symbol, K, comes from the Latin word kalium. It is now made from 
potassium chloride by the Leblanc or other processes. It is used 
extensively in the manufacture of hard glass, soft soap, caustic potash 
(potassium hydroxide), and other potassium compounds. 

467. Potassium hydroxide (KOH) resembles sodium 
hydroxide in properties. It is prepared from potassium 
chloride by the methods used for sodium chloride. Like 
sodium hydroxide, it dissolves readily in water with evo- 
lution of heat, forming a strongly alkaUne solution. Its 



374 PRACTICAL CHEMISTRY 

solutions corrode and disintegrate animal and vegetable 
matter and many mineral substances ; hence the term 
caustic potash. 

468. Other potassium compounds. — Potassium cyanide (KCN) 
and potassium sulphate (K2SO4) resemble the corresponding sodium 
compounds. 

Purified acid potassium tartrate (HKC4H4O6) is commonly known 
as cream of tartar. It is extensively used in the manufacture of 
tartrate baking powders. These are mixtures of cream of tartar and 
sodium bicarbonate (HNaCOs), together with a small proportion of 
starch (454). When dissolved in water or moistened by the water in 
a food mixture, the two ingredients interact and liberate carbon diox- 
ide as the main product, thus: — 

HKC4H4O6 + HNaCOs - COo + NaKC4H406 + HoO 

Acid Potas- Sodium Carbon Sodium Po- Water 

sium Tartrate Bicarbonate Dioxide tassium Tartrate 

469. Relation of potassium to life. — Potassium, like 
nitrogen and phosphorus, is essential to the life of plants 
and animals. The ash of many common grains, vegetables, 
and fruits contains potassium carbonate, which is formed 
from the complex organic potassium compounds in them. 
Potassium salts are taken from the soil by plants and must 
be returned if the soil is to be productive. Sometimes 
wood ashes, or the sulphate and chloride, are apphed to the 
soil. Usually the potassium salts are supplied in the form 
of fertilizer. Experiments show that many soils need po- 
tassium salts as plant food (Fig. 160). (Compare 116, 427, 
428.) 

EXERCISES 

1. Describe the manufacture of sodium. 

2. Summarize the physical properties and chemical conduct of 
sodium. 

3. Give an outline of the manufacture of sodium carbonate by 
(a) the Leblanc process, and (&) the Solvay process. Write the es- 



SODIUM AND ITS COMPOUNDS 



375 



sential equations for each pro- 
cess. 

4. What is (a) soda, (b) 
soda ash, (r) sodium carbonate, 

(d) soda crystals, (e) sal soda, 
(/) washing soda, (g) " alkali," 
(//) acid sodium carbonate, (/) 
saleratus, (j) baking powder, 
(k) baking soda, (/) caustic 
soda? 

5. Describe the manufac- 
ture of sodium hydroxide by 

(a) the chemical process and 

(b) the electrolytic process. 

6. What is a simple test for 
(a) sodium, and (b) potassium? 

7. How is potassium nitrate 
manufactured? 

8. Why does sodium car- 
bonate form an alkaline solu- 
tion? 

9. Topics for home study: 
(a) Davy. (b) Baking pow- 
ders, (c) Gunpowder, (d) Salt. 

(e) Food contains potassium 
compounds. 




Fig. i6i. — Result of an experiment 
with buckwheat. The pot on the 
left received a complete fertilizer, 
while the pot on the right diflFered 
only in receiving a fertilizer without 
potassium salts 



PROBLEMS 

1. Calculate the weight of sodium in (a) 20 gm. of XaOH, and 
(6) 22 gm. of acid sodium sulphate. 

2. Calculate the weight of potassium in (a) 15 gm. of KCl, and (b) 45 
gm. of potassium carbonate. 

3. Write the formulas of the sodium and potassium salts of the 
following acids : chloric, phosphoric (ortho), sulphurous, hydrofluoric, 
carbonic, acetic, hydrobromic, dichromic, permanganic, manganic. 

4. Give the name and formula of the ions in dilute solutions of 
(a) sodium hydroxide, (b) potassium nitrate, (c) sodium chloride, and 
(d) potassium sulphate. 



CHAPTER XXX 

CALCIUM CARBONATE — LIME — CEMENT- 
CALCIUM SULPHATE 

470. Occurrence of calcium compounds. — Calcium is 
never found free. Combined calcium makes up about 
3.5 per cent of the earth's crust (11). The most abundant 
compound is calcium carbonate (CaCOs). Many rocks are 
complex siHcates of calcium and other metals (383, 386). 
The extensive deposits of calcium phosphate (Ca3(P04)2) 
have been mentioned (420, 428). Calcium sulphate (CaS04) 
also occurs abundantly. 

Calcium compounds are essential to the life of plants and animals, 
being found in the leaves of plants, and in the bones, teeth, and shells 
of animals. Many rivers and springs contain calcium salts, espe- 
cially the acid carbonate (H2Ca(C03)2) and the sulphate. 

471. Calcium carbonate (CaCOs). — This is the most 
common calcium compound. The most abundant form 
is limestone ; vast beds are found in many regions. Pure 
limestone is white or gray, but impurities, especially or- 
ganic matter and iron compounds, produce many colored 
varieties. Much limestone contains silica, clay, iron and 
aluminium compounds, and the fossil remains of plants and 
animals. Hard, crystalline limestone which takes a good 
polish is called marble ; it is extensively used as a building 
and an ornamental stone. Calcite is the purest form of 
crystallized calcium carbonate ; a transparent variety called 
Iceland spar has the property of double refraction, i.e. 
of making objects appear double. 

376 



CALCIUM COMPOUNDS 



377 




Different grades of cal- 
cium carbonate are used 
in malting lime, cement, 
iron, glass, and sodium 
carbonate. 

472. Deposition of calcium 
carbonate. — Calcium car- 
bonate is practically insolu- 
ble in water. But if water 
contains carbon dioxide the 
carbonate dissolves, owing to 
its transformation into the 
soluble acid calcium carbon- 
ate (H2Ca(C03)o) (293). 
Many underground waters 
contain carbon dioxide, and 
as this water works its way 
along in limestone regions, 
the limestone is dissolved 
and caves are often formed 
or enlarged. When the water 
enters a cave and drips from 
the top, the water evaporates, or the gas escapes, or both, and calcium 
carbonate is redeposited, often forming stalactites and stalagmites. 
The stalactites hang from the roof like icicles, and are often exqui- 
sitely shaped ; the stalagmites, which grow up from the floor, some- 
times meet the stalactites and form a column (Fig. 162). Mexican 
onyx is a variety of stalagmite. Vast deposits of this beautiful mineral 
are found in Algeria and Mexico. It is translucent and delicately 
colored, and is used as an ornamental stone, especially for altars, table 
tops, mantles, soda fountains, and lamp standards. Travertine is 
another variety ; it occurs near many springs in Italy. When fresh it 
is soft and porous, but it soon hardens and becomes a durable building 
stone in dry climates. A portion of the walls of the Colosseum 
and St. Peter's is travertine. 

Calcium carbonate dissolved in the ocean is transformed by marine 
organisms into shells and bony skeletons. The hard parts of these 
animals accumulate in vast quantities on the ocean bottom, become 



Copyright by J. D. Strickler. 
Fig. 162. — Interior of a limestone 
cave at Luray. \'a., showing 
stalactites and stalagmites 



378 



PRACTICAL CHEMISTRY 



compact, often hardened and crystallized, and subsequently form a 
part of the land. Chalk is the remains of shells of minute anima's. 




Fig. 163. — Ooze from the ocean bottom showing limestone shells (left), 
and the same kind of shells (magnified) from chalk deposits in 
Iowa (right) 

When examined under a microscope, a good specimen is seen to con- 
sist almost entirely of tiny shells (Fig. 163). 

Limestone often contains fossils, confirming the belief that lime- 
stone is the remains largely of the shells of animals (Fig. 164, left). 
On the coast of Florida, coquina or shell rock is found (Fig, 164, right). 




Fig. 164. — Limestone containing fossils (left). Coquina (right) 



It is a mass of fragments of shells cemented by calcium carbonate, 
and in time will become compact limestone (164, right). 



CALCIUM COMPOUNDS 379 

Coral is calcium carbonate, and the vast accumulations in the sea 
are the skeletons of the coral animals. 

473. Chemical conduct of calcium carbonate. — Cal- 
cium carbonate is decomposed by heat into lime (CaO) 
and carbon dioxide (475). It interacts with acids, thus : — 

CaCOa + 2HCI = CaCl, + H>0 + C0,> 

Calcium carbonate itself is precipitated by the interaction 
of a soluble calcium salt and a soluble carbonate, thus : — 



CaCb 


+ NaoCOs 


= CaCOa 


+ 


2XaCl 


Calcium 


Sodium 


Calcium 




Sodium 


Chloride 


Carbonate 


Carbonate 




Chloride 



Purified calcium carbonate prepared this way is called precipitated 
chalk, and is used extensively as the polishing ingredient of tooth 
powder. An impure variety is called whiting : a mixture of whiting 
and linseed oil is putty. 

474. Lime. — This famihar substance is calcium oxide 
(CaO). It is a hard, white solid. Pure hme is almost in- 
fusible, and when heated in the oxy hydrogen flame, it gives 
an intensely bright Hght, called the lime light (57). In 
the intense heat of the electric furnace it melts (at about 
2750° C.) and at a higher temperature it boils. 

Lime when exposed to the air becomes "air slaked," 
i.e. it slowly absorbs w^ater and carbon dioxide, swells con- 
siderably, and soon crumbles to a powder. This powder is 
a mixture of calcium hydroxide and calcium carbonate ; 
such a mixture is not suitable for many of the uses of Hme. 
(Compare hydrated lime, 476.) Lime that is not air slaked 
is called quicklime or caustic lime. When just the riirht 
amount of water is slowly added, the product is calcium 
hydroxide or hydrated Hme (476). If an excess of water 
is added quickly, lime and water combine readily and vigor- 
ously ; considerable heat is Hberated, as is seen when mor- 



38o PRACTICAL CHEMISTRY 

tar is being prepared. This operation is called slaking, 
and the product is slaked lime. The thermo-chemical 
equation is : — 

CaO + H2O = Ca(0H)2 + 15,540 calories 

Calcium Oxide Water Calcium Hydroxide 

Sometimes water leaks into barrels, cars, or buildings in 
which lime is stored, and the heat evolved causes a fire. 

Lime has many indispensable uses. Immense quantities 
are consumed in preparing mortar, plaster, and cement. 
Many useful chemicals are made from Hme, e.g. bleaching 
powder (149), calcium carbide (295), sodium hydroxide 
(456), calcium bisulphite (263), hme-sulphur mixtures (248), 
and calcium cyanamide (CaN2C) (484). Much is used in 
such industrial operations as purifying illuminating gas, 
refining sugar, softening water, removing hair from hides, 
bleaching cotton cloth, extracting metals from ores. In 
agriculture it is added to soil to neutralize acids. 

475. Manufacture of lime. — Lime is manufactured by 
heating Hmestone in a partly closed cavity or in a furnace. 
(Either one is called a kiln.) The decomposition takes 
place according to the equation : — 

CaCOs = CaO + CO2 

Calcium Carbonate Calcium Oxide Carbon Dioxide 

The carbon dioxide escapes ; the Hme is left in the kiln. 

Limestone was formerly " burned " in a cavity on a hillside, and 
in some regions it is so prepared today. An arch of limestone is 
built across the cavity above the fire pit, and limestone is introduced 
until the kiln is full. 

The arch kilns have been largely replaced by furnaces (Fig. 165). 
The heat is produced by burning gases (at B, B). The hot air and 
gaseous products of combustion pass up through the limestone (fed 



CALCIUM COMPOUNDS 



38t 




Fig. 165. — Sketch of a contin- 
uous limekiln 



in at .1) and heat it to the proper 
temperature (about 750 to 900° C). 
The rising gases sweep out the car- 
bon dioxide, thus aiding the process. 
The solid sinks down through the 
furnace and is removed frequently 
(at C, f). The towers of mod- 
ern kilns are 60 feet or more high 
(Fig. 166). They operate contin- 
uously and produce from 25 to 60 
tons a day according to size. Sev- 
eral towers are often connected 
with a single gas producer. 

476. Calcium hydroxide 

(Ca(0H)2) is a white solid. 
It is manufactured by adding 
carefully just enough water 

to calcium oxide to produce the hydroxide. This hydrated 
lime, as it is called, is a fine, white powder. If properly 
packed, it will keep indefinitely. Also, it can be stored 
without danger of causing fire. It is suitable for the same 

purposes as the lime 
slaked just before use. 



Calcium hydroxide is spar- 
ingly soluble in water, but 
more soluble in cold than in 
warm water (79) . The solu- 
tion has a bitter taste and 
a mild alkaline reaction ; it 
is often called limewater. 
Exposed to the air, lime- 
water becomes covered with 
a thin crust of calcium car- 
bonate, owing to interaction 
with carbon dioxide. For the 
same realson, limewater be- 




Fig. 166. 



A modern 
operation 



limekiln in 



382 PRACTICAL CHEMISTRY 

comes milky or cloudy when carbon dioxide is passed into it. The 
formation of calcium carbonate in this way is, the test for carbon 
dioxide (1). 

477. Lime water is prepared by carefully adding lime to con- 
siderable water, allowing the mixture to stand in a stoppered bottle 
until the solid has settled, and then removing the clear liquid. When 
considerable calcium hydroxide is suspended in the liquid, the mix- 
ture is called milk of lime. Ordinary whitewash is thin milk of lime. 

478. Mortar is a thick paste formed by mixing lime, 
sand, and water. It slowly hardens or " sets " without 
much shrinking, owing to loss of water and to interaction 
with carbon dioxide. When placed between bricks or 
stones it holds them firmly in place, and is used to construct 
buildings, walls, foundations, etc. 

The sand gives bulk and rigidity ; it also makes the mass porous 
and thus facilitates the change of the hydroxide to the carbonate. 
We can readily prove that a carbonate is formed by adding hydro- 
chloric acid to a lump of old mortar ; the liberated gas is carbon di- 
oxide. Hair is sometimes added to make the mortar stick better, 
especially when it is used as plaster for walls. Hair is not necessary, 
if cement (479) is mixed with the mortar. 

479. Cement is a kind of strong, firm mortar. Like 
ordinary mortar, it hardens in the air ; unlike mortar, how- 
ever, it has the pecuHar and useful property of hardening 
even under water. 

The chemical changes which occur in the setting of 
cement are complex and not well understood. The prod- 
ucts, whatever they are, set into a very hard mass. 

Cement is next to iron and steel in importance as a build- 
ing material. Immense quantities (about 100,000,000 bar- 
rels annually) are used in a great variety of structures — 
foundations, dams, bridges, fireproof buildings (e.g. 
garages), storage tanks, warehouses, floors, walks. A mix- 
ture of cement, sand, water, and crushed stone is known as 



CALCIUM COMPOUNDS 



383 



concrete, which is used, usually instead of cement alone, 
as construction material. Sometimes concrete is strength- 
ened by imbedding rods of steel in it ; it is then called re- 
enforced concrete. 

480. Manufacture of cement. — Cement is made from 
natural or, more commonly, artilicial mixtures of limestone 




Fig. 167. — Rotary kilns for making cement 

and clay. The raw materials must contain the propor- 
tions of the essential ingredients, viz. limestone, clay (alu- 
minium silicate), and sand, which have been found by ex- 




Plg. i6S. — Sketch of a cement kiln 

perience to give the best results. The materials are mixed, 
ground very fine, and fed into a long furnace made of steel 
and lined with fire-brick. The furnace is sHghtly incUned 
and rotates slowly (about once a minute) ; it is called a 
rotary kiln (Fig. 167). 



384 PRACTICAL CHEMISTRY 

The process can be best understood by studying the simple sketch 
in Fig. 168. The mixture enters at the upper end (C). As it gradu- 
ally works its way along through the slowly rotating kiln, it is heated 
by the flame and hot gases produced (inside the kiln) by burning oil 
or coal dust, which is forced in at A by a powerful air blast. The 
mixture forms a semifused, gray-black mass which drops out at B. 
The cooled lumps, called clinker, are mixed with about 2 per cent 
of gypsum (calcium sulphate, 481), and ground to a very fine 
powder. This powder, which is grayish, is cement; it is often 
called Portland cement. 

481. Calcium sulphate (CaS04). — Extensive deposits 
of difTerent forms of calcium sulphate are found in many 
localities ; in the United States large quantities are ob- 
tained in New York, Michigan, and the Middle West. 
Gypsum is the commonest form; it occurs as white masses 
which have the composition CaS04.2H20. A translucent 
variety of gypsum is called selenite. The mineral anhy- 
drite is anhydrous calcium sulphate (CaS04). Gypsum 
is used as an ingredient of some fertilizers and in making 
plaster of Paris, paper, white paint, and cement. 

482. Plaster of Paris is a fine white powder made by heating 
gypsum to the proper temperature (about 145° C). The equation 
is: — 

2CaS04.2H,0 = (CaS04)2.H20 -f 3H2O 

This powder has the composition (CaS04)2-H20. If moistened with 
water, it swells and quickly sets or solidifies to a hard mass which con- 
sists of a netw^ork of very small crystals. The equation for the setting 
^f plaster of Paris may be written : — 

(CaS04)2.H20 + 3H2O = 2CaS04.2H20 

Plaster of Paris Water Gypsum 

Plaster of Paris is used to coat plastered walls, to cement glass 
to metal, but more largely to make casts and reproductions of 
statues and small objects. Stucco is a mixture of glue and plaster of 
Paris. 



CALCIUM COMPOUNDS 



38; 




483. Calcium compounds and hardness of water. — 

Calcium sulphate is slightly solul)le in water, and calcium 
carbonate, as we have already seen, is changed into soluble 
acid carbonate by water containing carbon dioxide. Water 
containing these salts is called hard water. And water 
from which they are absent is often called soft 
water. 

Soap does not dissolve readily in hard water, but forms 
sticky, insoluble compounds with calcium (and magnesium) 
salts ; hence a large quantity of soap must 
be used up before a lather will form. 

Hard water, if used in boilers, forms 
deposits on the inside of the boiler tubes, 
thus causing waste of heat (Fig. 169) ; in 
some cases acids {e.g. HCl) are liberated 
which corrode the boiler. 

Hardness due to acid calcium carbonate 
(or acid magnesium carbonate) is called 
temporary hardness, because boiling re- 
moves it. Temporary hardness can also 
be removed by adding calcium oxide or hy- 
droxide to change the soluble acid carbon- 
ate to the insoluble carbonate. After either method, the 
water must be filtered, or siphoned off, to get rid of the 
calcium carbonate. 

Water containing calcium sulphate or chloride is said 
to have permanent hardness, because these salts cannot 
be removed by boihng. (Magnesium sulphate and chloride, 
like the corresponding calcium salts, produce permanent 
hardness.) Permanently hard water can be softened by 
adding sodium carbonate (e.g. ordinary washing soda), 
which converts the calcium (and magnesium) salts into 
insoluble carbonates, thus : — 



Fig. 169. — Sec- 
tion of a boiler 
tube showing 
the scale de- 
posited by 
hard water 



386 PRACTICAL CHEMISTRY 



CaS04 + NasCOa -■ 


= CaCOs 


+ Na2S04 


Calcium Sodium 


Calcium 


Sodium 


Sulphate Carbonate 


Carbonate 


Sulphate 



This process is used on a large scale to soften boiler water. 
In the home, borax or ammonia may be used. 

Several processes are used to soften boiler water. A recent one 
utilizes the fact that substances called pennutit (essentially an arti- 
ficial sodium silico-aluminate) will interact with calcium (and mag- 
nesium) compounds, and thereby remove them from the water. The 
w^ater filters through a porous layer of the permutit, and the calcium 
(and magnesium) replaces the sodium. A conventional equation 
might be written thus : — 

Calcium Sodium _ Calcium . Sodium 

Sulphate Permutit ~ Permutit Sulphate 

After a time, the calcium permutit accumulates to such an extent 
that the mixture no longer reacts. Water containing sodium chloride 
is then added and allowed to remain long enough to regenerate the 
sodium permutit, thus : — 

Calcium Permutit -}- 2NaCl = Sodium Permutit 4- CaCl2 

The calcium chloride is removed, and the filter is ready for use again. 
This regenerative process can be repeated, thereby permitting the 
use of the original charge of permutit many years. Water softened 
by this process contains practically no calcium (or magnesium) salts. 
484. Other calcium compounds. — Important calcium compounds 
already described are the fluoride, carbide, phosphates, and hypo- 
chlorite (bleaching powder). Calcium chloride (CaCy is used to 
dry gases and liquids (85). It is a by-product in the manufacture of 
sodium carbonate by the Solvay process (450) . A solution of calcium 
chloride is used as a brine in the manufacture of ice (177). Calcium 
sulphide (CaS) is formed by reducing calcium sulphate with carbon ; 
like other sulphides, it stains silver brown (274). Calcium oxalate 
(CaC204) is a white solid formed by the interaction of ammonium 
oxalate and a dissolved calcium compound ; it is insoluble in acetic 
acid but soluble in hydrochloric acid. Its formation and properties 
serve as a test for calcium. Another test for calcium is the orange- 



CALCIUM COMPOUNDS 



387 



red color imparted to the Bunsen llame. Calcium nitrate (Ca(NO;02) 
and calcium cyanamide (CaNjC) are made from the nitrogen of the air, 
and are used as fertilizers because they provide nitrogen in a form 
easily taken up by plants. The commercial substances are dark 
solids. For the nitrate see 196. The cyanamide is made by passing 
nitrogen over very hot calcium carbide, the equation being : — 



N2 + CaCo 

Nitrogen Calcium Carbide 



CaXoC + 

Calcium Cyanamide 



c 

Carbon 



485. Preparation and properties of metallic calcium. 

Metallic calcium is prepared by the 
electrolysis of melted calcium chlo- 
ride (Fig. 170). 

The anode is a graphite crucible (^1) and 
the cathode is a rod of iron (B), which 
dips into the melted calcium chloride a short 
distance and is adjusted so that it can be ele- 
vated by a screw (C) . The lower part of the 
crucible, which is kept cool by running water 
(£, E), contains solid calcium chloride. 
When the current passes, calcium is de- 
posited on the cathode, which is slowly 
raised so that its end only is in contact with 

the surface of the melted chloride; the js-^=^ '^^=^E 

irregular rod of deposited calcium {D) thus pjg^ j^q. — Apparatus 
becomes the end of the cathode. for preparing calcium 

by electrolysis 

Calcium is a silvery white metal. 
It tarnishes slowly in air. When heated, it combines 
with most non-metals. If burned in air, it forms both 
the oxide (CaO) and the nitride (Ca3X2). It interacts 
with water, slowly at ordinary temperatures, rapidly at 
high temperatures, thus : — 




Ca + 
Calcium 



2H,0 = Ca(0H)2 + He 

Water Calcium Hydroxide Hydrogen 



388 PRACTICAL CHEMISTRY 

It also interacts readily with acids, thus : — 

Ca + 2HCI - CaClo + H2 

Calcium Hydrochloric Acid Calcium Chloride Hydrogen 

486. Compounds of strontium and barium. — Com- 
pounds of these elements resemble the corresponding ones 
of calcium. Strontium nitrate (Sr(N03)2) and other salts 
of strontium color a flame crimson ; the nitrate is used in 
making red signal lights and fireworks, especially red fire. 
The latter is essentially a mixture of potassium chlorate, 
shellac, and strontium nitrate. The production of the crim- 
son colored flame is a test for strontium. Another test is the 
precipitation of white strontium sulphate by the addition 
of calcium sulphate solution to a strontium salt solution. 

Barium chloride (BaClo) is used in testing for sulphuric 
acid and soluble sulphates, because it readily interacts 
with them and forms insoluble barium sulphate (BaS04) ; 
conversely, this serves as the test for barium. 

Barium sulphate is a fine, white powder, and being cheap and 
heavy it is a common adulterant of ordinary white paint. Ground 
native barium sulphate, often called barytes, has a similar use. 
Barium sulphate is also used to increase the weight of paper and to 
give it gloss. 

Barium salts color a flame green and barium nitrate 
•(Ba(N03)2) is used in making fireworks, especially green 
fire. The production of the green flame is a test for barium. 
Barium chromate (BaCr04) is a yellow precipitate formed 
by the interaction of potassium dichromate (or potassium 
chromate) and a soluble barium compound ; its formation is 
sometimes used as a test for barium. 

EXERCISES 

1. Name several native compounds of calcium. What proportion 
of the earth's crust is calcium? Compare this proportion with that of 
other abundant elements (11). 



CALCIUM COMPOUNDS ^89 

2. Review topics: (a) The properties of normal ancj acid cal- 
cium carbonate. (/') Calcium com.pounds previous'/ studied. 

(c) Compare the manufacture of calcium and sodium. 

3. Topics for home study : (a) Does limestone " burn " ? (b) Is 
the term linuicater accurate? Why? (r) How should lime be stored? 

(d) Compare the setting of plaster of Paris and mortar, (e) Uses of 
cement. (/) Suggest experiments to show that lime is calcium oxide. 

4. State the properties and uses of lime. How is it made? 

5. Describe the manufacture of cement. 

6. Starting with calcium, how would you prepare successively the 
oxide, hydroxide, carbonate, chloride, and metal? 

7. What is plaster of Paris? Wh}' so called ? How ir it prepared ? 
What is its chief property? What are its uses? What is the chemical 
explanation of " setting " ? What is stucco? 

8. What is hard water? How does it act with soap? What is 
(a) temporary hardness and (b) permanent hardness? How can each 
be removed? What is soft water? Why is rain water often called 
soft water? 

9. Essay topics: (a) Famous limestone caves, (b) The cement 
industry, (c) Colored fireworks, (d) Industrial uses of lime. 

(e) Chalk. (/) Coral, (g) Boiler scale. 

10. Write equations for the reactions necessary to prepare (a) 
barium nitrate from barium carbonate, (b) barium hydroxide from barium 
chloride, (c) strontium carbonate from strontium hydroxide. 

11. State the flame tests for (a) calcium, (b) strontium, and 
(c) barium. 

PROBLEMS 

1. How many grams of calcium can be obtained from (a) 150 gm. 
of calcium chloride, (b) i kg. of Iceland spar? 

2. Calculate the percentage composition of the two o.xides of barium 
(BaO and BaOi) and show that they illustrate the law of multiple pro- 
portions. (Use exact atomic weights.) 

3. Calculate the simplest formula from the following data : Ca = 
29.49, O = 46.92, S = 23.59. 

4. How many tons of lime can be made from 2000 tons of limestone 
(95 per cent pure) ? 

5. Write the formulas of the following compounds by applying 
the principle of valence : Calcium chlorate, calcium permanganate, 
calcium fluoride, calcium (meta-) silicate, calcium sulphide. 

6. Calculate the atomic weight of calcium from 31.207O2 gm. of 
CaCOs give 17.49526 gra. of CaO. 



390 PRACTICAL CHEMISTRY 

7. Express the following reactions by equations : (a) Carbon diox- 
ide, water, and calcium carbonate form ; (b) barium hydroxide 

and carbon dioxide form and water; (c) strontium carbonate 

forms and carbon dioxide. 

8. Express the following interactions in the form of complete 
ionic equations : (a) calcium chloride and sulphuric acid; (b) ammo- 
nium carbonate and strontium chloride; (c) barium chloride and potas- 
sium chromate. 



CHAPTER XXXI 

IRON AND STEEL — IRON COMPOUNDS 

487. Introduction. — Iron is one of the oldest metals. 
It is also the most useful, and has been indispensable in 
the development of the human race. The different kinds 
of steel that are manufactured from iron have made the 
present times an age of steel. 

488. Occurrence of iron. — In abundance iron ranks 
fourth among the elements and second among the metals 
(11). Uncombined iron is found in meteorites. Combined 
iron is found in most rocks, soils, and natural waters. It 
is assimilated by plants and animals and is essential to 
their life processes, being a constituent of chlorophyll (the 
green coloring matter of plants) and of hemoglobin (the red 
coloring matter of blood). 

Metals usually occur as compounds, e.g. oxides, sulphides, 
or carbonates. A mineral or rock from which the metal 
can be more or less profitably prepared is called an ore. 
The important ores of iron are hematite (FcoOa), limonite 
(2Feo03.3H20), magnetite (Fe304), and siderite (FeCOa). 
The most abundant ore and the chief source of iron and 
steel is hematite, which comes mainly from the Lake Supe- 
rior region. Large quantities of iron ore are also mined in 
Alabama, Tennessee, and the Virginias. 

Other abundant compounds of iron, not, however, used as a source 
of this metal, are iron pyrites (FeSj), pyrrhotite (varying from FeeS; to 
FeiiSi2), and the copper-iron sulphides (chalcopyrite, CuFeS2, and 
bornite, CusFeSa, 526, 527). 

391 



392 



PRACTICAL CHEMISTRY 



489. How iron is obtained from its ores. — The science 
of extracting metals from their ores is called metallurgy. 
Iron is obtained by reducing its oxides with carbon. The 

ore is mixed with a flux 
(usually Hmestone) and 
carbon (usually in the form 
of coke) and heated in a 
furnace. This process is 
called smelting. The car- 
bon together with carbon 
monoxide reduces the ox- 
ide to metalHc iron. The 
flux converts the mineral 
impurities in the ore, called 
gangue {e.g. sihcon and 
aluminium compounds), 
into fusible silicates called 
slag. The operation is 
carried out in a blast fur- 
nace (Figs. 171, 172). 

The blast furnace, as shown 
in the sketch (Fig. 171), is a 
tower, about ninety feet high 
and twenty feet in diameter 
at the largest part ; it is nar- 
rower at the top and bottom 
than in the middle. It is built 
of steel and Hned with fire brick. 
Near the bottom are pipes, 
called tuyeres, through which 
large quantities of hot, dry air are forced into the furnace, thereby 
producing the high temperature required in the smelting. The air 
is heated, before it enters, by the stoves (the chimney-like towers 
between the furnaces shown in Fig. 172). 

Another pipe at the top permits the escape of hot gaseous products, 




Fig. 171. — Sketch of a blast fur- 
nace and the process of smelting 
iron ore 



IRON AND STEEL 



393 




Fig. 172. — Blast furnaces and stoves 



and also conducts them into a scries of pipes which lead to dif- 
ferent parts of the plant, where the hot gases are utilized to heat 
the air (in the stoves) blown through the tuyeres, and also as fuel. 

When the blast furnace is in operation, charges of the 
proper proportions of ore, coke, and flux are introduced at 
intervals by dumping them upon the cone-shaped cover. 
The latter is constructed and operated so that the smelting 
is not interrupted. The hot air which enters at the bottom, 
through the tuyeres, changes most of the carbon in the 
lower part of the furnace into carbon dioxide and thereby 
generates intense heat. The carbon dioxide is largely 
reduced by the hot carbon above it to carbon monoxide, 
which rises through the furnace and reduces the iron oxide 
to iron. As the smelting proceeds, the reduction continues 
and the flux forms a slag (largely calcium silicate). Both 
iron and slag sink, the molten iron finally falling through 
the slag to the bottom of the furnace, where each is 
drawn off through separate openings at desired intervals (as 
shown in Fig. 171). 



394 



PRACTICAL CHEMISTRY 



The chemical changes during the smelting vary in different zones. 
In the top zone the moisture in the charge is removed. In the second 
zone, where the temperature rises above 800° C, carbon monoxide 
interacts with the iron ore and forms a mixture of iron and ferrous 
oxide (FeO). These reactions are expressed thus: — 



sFe.A 

Ferric Oxide 



+ CO = 2Fe304 -f CO2 

Carbon Monoxide Ferrous-ferric Oxide Carbon Dioxide 



Fe304 4 

Ferrous-ferric Oxide 



CO 



3FeO + 

Ferrous Oxide 



CO2 



FeO + 

Ferrous Oxide 



CO 



Fe 

Iron 



CO, 



At this stage the ore, though not wholly reduced, becomes soft and 
porous and sinks down into the third zone. The temperature here is 
about 1300° C. The reduction of the ferrous oxide is completed, 
hastened no doubt by the action of the hot carbon, thus : — 

FeO + C = Fe + CO 

Here, too, certain impurities, present in small proportions in the ore, 
are changed to elements, e.g. manganese, siHcon, phosphorus, and sul- 
phur, which unite with 
the iron. In the last 
zone, where the tempera- 
ture rises to 1500° C, 
the iron fuses com- 
pletely, takes up some 
carbon, and sinks down 
to the bottom of the fur- 
nace. In this zone, too, 
the reactions occur which 
complete the formation 
of slag, which is essen- 
tially a mixture of cal- 
cium silicate and calcium 
aluminate. 

The molten slag, which 
Fig. 173 — Tapping a blast furnace floats on the molten 




IRON AND STEEL 395 

iron, is tapped off at intervals. The iron is tapped off into huge 
ladles (Fig. 173). Sometimes it is run from the furnace into molds 
of sand or iron {i.e. in a casting machine) and allowed to solidify ; 
such iron is called cast iron or pig iron. In some plants the molten 
iron is run directly into huge vessels, called converters, and made 
into steel (493). 

490. Cast iron. — The metal that comes from a blast 
furnace is impure iron. Besides iron, it contains from 3 to 
5 per cent of carbon, i to 3 of siUcon, about 0.7 each of man- 
ganese and phosphorus, and 0.02 to 0.05 of sulphur. 

The properties of cast iron depend largely on the pro- 
portion of carbon and on the rate at which the molten iron 
cooled. If the cooHng takes place rapidly (as in the cast- 
ing machine), most of the carbon is combined with the iron 
as a carbide (FcsC), called cementite. This variety of cast 
iron is called white cast iron. But if the cooling occurs 
slowly (as in sand molds), much of the carbon remains un- 
combined as scales of graphite. This variety of cast iron 
is known as gray cast iron. It is softer and less brittle 
than the white variety, and melts at a lower temperature. 

Cast iron has a crystalline structure and is brittle ; it 
will withstand great pressure. It cannot be welded nor 
forged, that is, hot pieces cannot be united nor be shaped 
by hammering. But it can be cast, i.e. it can be formed 
into a desired shape by pouring the molten metal into a 
mold. 

Cast iron is the variety used in an ordinary iron foun- 
dry. Here the iron, which melts at about 1200° C, is 
heated in a furnace similar to a blast furnace, and when 
molten is poured into sand molds of the desired shape. 
Stoves, pipes, pillars, railings, radiators, parts of machines, 
and many other useful objects are made of cast iron. Con- 
siderable cast iron is made into steel (493). 



396 



PRACTICAL CHEMISTRY 



Cast iron to which 5 to 20 per cent of manganese has been 
added is called spiegel iron, while ferro-manganese contains 
20 or more per cent of manganese ; both are used in making 
steel. 

Ca^t iron is not attacked by alkalies and only shghtly 
by concentrated acids. Concentrated sulphuric acid is 
transported in iron tank cars. Cast iron interacts readily, 
however, with dilute acids. 

491. Wrought iron. — Wrought iron is made from cast 
iron by removing most of the impurities (carbon, silicon, 

phosphorus, and sulphur). 
This can be done by heat- 
ing the cast iron with iron 
oxide. 

The process is conducted 
in a reverberatory furnace 
(Fig. 174). The hearth (5), 
of the furnace is covered with 
iron ore (ferric oxide, FcoOs) 
and the charge of cast iron 
and flux is laid upon it. The 
intense heat that is reflected 
down upon the charge by the 
roof of the furnace melts the 
cast iron. The carbon in the 
cast iron unites with the oxy- 
gen of the iron oxide and es- 
capes as carbon monoxide. The silicon and phosphorus are oxidized 
and react with the flux to form a slag ; the manganese and sulphur 
(in the form of ferrous sulphide) also become a part of the slag. 
The mixture is stirred or " puddled " with long rods, and as the im- 
purities are removed, the mass becomes pasty owing to the rise of 
its melting point. 

Large balls, called blooms, are removed and hammered, or, more 
often, rolled between ponderous rollers. The operation squeezes 
out most of the slag. If the rolling is repeated, the quality of the 




Fig. 174. — Reverberatory furnace. 
The fire burns on the grate G, and 
the long flame which passes over 
the bridge E, is reflected down by 
the sloping roof upon the con- 
tents of the furnace. Gases escape 
through. The charge, which rests 
upon B, does not come in contact 
with the fuel 



IRON AND STEEL 



397 



iron is improved ; the final roiling often leaves the iron in the desired 
commercial shape. 

Wrought iron is the purest variety of commercial iron. 
It is practically pure iron, containing only 2 per cent (or less) 
of slag (Fig. 174, left). The iron itself seldom contains 
more than 0.5 per cent of carbon and sometimes only 0.06 
per cent, the average being about 0.15 per cent; the other 
elements are present in mere traces. 

If a specimen of wrought iron, or other metal, is polished and then 
etched with weak acid, the microscope reveals the crystalline or other 





d 






-Em. . 


s.,. « 


«C^' d. 




jJfl*'* • l^'^-T / 


• - -^ 


r'^Qv i/^ ^ 




^s->^4 ^^-^^ 


■» 


^-i-^.-^^&C.^--'- 


^Z*r^. 



*v?yvn 



-^^ 



Fig- 175- — Photomicrographs of wrought iron (left) and cast iron 
(right). The slag can be seen in the wrought iron 

formation and the presence of carbon, slag, carbides, etc. Photo- 
graphs of a treated specimen of wrought iron and cast iron as seen 
under the microscope are shown in Fig. 175. 

Wrought iron, unlike cast iron, is fibrous and can be bent. 
It melts at a higher temperature than cast iron (1600*^ to 
2000° C). Since it softens at about 1000° C, wrought iron 
can be forged and welded. It is very malleable and ductile, 
can be readily rolled into plates and sheets and drawn into 
fine wire.; in these forms the metal is very strong. 
Wrought iron is made into wire, sheets, rods, nails, spikes, 



398 



PRACTICAL CHEMISTRY 



bolts, chains, anchors, horseshoes, tires, and agricultural 
implements. It is less important than formerly, since it 
is being replaced by soft steel (498). 

Wrought iron rusts more rapidly than cast iron, and is 
also more vigorously attacked by acids and alkahes at a 
high temperature. 

492. What is steel ? — We have just seen that cast iron 
is hard and brittle, whereas wrought iron is soft and tough. 
Also, that cast iron can be easily melted and poured into 
molds, whereas wrought iron softens readily and can be 
welded. Moreover, cast iron contains a relatively high 
per cent of carbon (3 to 5), but in wrought iron the per cent 
of carbon is low (0.15). Between these extremes of com.po- 
sition come the different grades of steel. 

The physical properties of the different grades of steel 
depend not only on the proportions of carbon, phosphorus, 
silicon, sulphur, etc., but also to a large extent on the 
method of manufacture and treatment. 

493. Manufacture of steel. — Steel is made from cast 
iron. The aim in the manufacture is to prepare a product 
containing the desired proportion of carbon but httle or 
no sulphur, phosphorus, and sihcon. The steel must also 

possess specific and known 
properties. This twofold 
aim is accomplished by 
several processes. 

494. The Bessemer 
process is carried on in 
a converter (Fig. 176). 
This is a huge, pear- 
shaped vessel, supported 
on trunnions so it can 
Fig. 176. — Sketch of a converter be tipped into different 



Air- 




IRON AND STEEL 399 

positions; one trunnion is hollow, and at the bottom there 
are holes (C, C\ C), through which a powerful ])last of 
air can. be blown. It is made of thick wrought-iron 
plates and is lined with an infusible mixture rich in silica. 

The converter when in use is swung into a horizontal 
position, and fifteen to twenty tons of molten cast iron 
are run in, often directly from the blast furnace (Fig. 177, 
right). The air blast is turned on, and the converter is 
swung back to a vertical position. As the air is forced in 
fine jets through the molten metal, the temperature rises, 
and the carbon, silicon, and manganese, that are in the 
iron, are oxidized. The carbon forms carbon monoxide, 
which burns at the mouth of the converter in a large bril- 
liant flame (Fig. 177, left), while the other oxides pass 
into the slag. This oxidation generates enough heat to 
keep the metal melted. In about fifteen minutes the di- 
minished flame of burning carbon monoxide shows that the 
carbon has been oxidized and the other impurities removed. 
Then sufficient spiegel iron or ferro-manganese is added to 
the molten iron to furnish the proper amount of carbon 
and manganese. By adding certain metals, e.g. aluminium, 
gases are removed (by uniting with the metal), and a better 
quaUty of steel is produced. 

After the completion of the whole operation the con- 
verter is tilted and the metal is poured into ladles, and then 
into molds to form blocks called ingots (Fig. 177, left fore- 
ground), which are subseciuently shaped into rails or other 
objects (Figs. 183, 184, 185). 

The process described in the preceding paragraph is called the 
acid Bessemer process because the converter is lined with silica, 
which is an acid anhydride (388). By this process the carbon and 
silicon can be removed but not all the sulphur and phosphorus. Both 
are objectionable. Sulphur makes steel brittle when hot, and phos- 



400 



PRACTICAL CHEMISTRY 




IRON AND STEEL 



401 



phorus, when cold. The acid Bessemer process is used in the United 
States because most domestic ores are low in phosphorus and sulphur. 
In Europe the Thomas-Gilchrist or basic process is used. The 
converter in this modilied process is lined with burned dolomite {i.e. 
practically a mixture of lime and magnesia, which are basic oxides), 
which removes the phosphorus and sulphur. This lining after use 
is known as Thomas slag. It is utilized as a fertilizer on account 
of its phosphorus content. 

495. The open-hearth process. — This process is con- 
ducted in a special kind of furnace called an open-hearth 
furnace (Fig. 178). A vertical section of an open-hearth 




Fig. 178. — General view of open-hearth furnaces in a steel plant 

furnace is shown in Fig. 179. The hearth (H), on which 
the charge is put, is lined with burned dolomite. A sloping 
roof of fire brick covers the hearth. At the base of the fur- 
nace are dupUcate chambers of checkerwork {A, B and 
C, D) arranged for alternate use. This arrangement is 
necessary in order to obtain continuously the high temper- 
ature needed in this process. 

Fuel gas (or oil) is burned in a furnace and the hot gases 
are passed through A, B to the chimney, thus heating 
the checkerwork very hot. The fuel gas is then passed 



402 



PRACTICAL CHEMISTRY 




Fig. 



179. 



Sketch of an open-hearth furnace 
(vertical section) 



through B and 
air through A 
and the two 
brought to- 
gether over the 
hearth. Here 
the gas burns 
and produces a 
high tempera- 
ture on the 
hearth. ISIean- 
while the hot 
products of com- 
bustion and the 
unused gases, 
instead of escaping immediately up the chimney, are di- 
rected by valves through the other two chambers of the 
checkerwork C, D, and heat them. That is, while A, B 
are cooling, C, D are heating. At the proper time the 
fuel gas and air are shifted (by valves) to C, D and made 
through this 



to pass 
checkerwork to the 
hearth and out over the 
other checkerwork {A , 
B) to the chimney. 

By this plan the pro- 
cess is alternated, one 
checkerwork being cooled 
as the other is heated, 
and vice versa. It is 
only by this regenerative 
process, as it is called, 
that enough heat is ob- 




Fig. 180. — Pouring molten cast iron 
into an open-hearth furnace 



IRON AND STEEL 



403 



tained continuously to 
keep the charge melted 
as it becomes purer and 
purer. 

The charge consists of 
cast iron and some iron 
oxide {e.g. hematite) ; 
scrap iron, or steel, and 
hme are usually added 
(Fig. 180). The iron ox- 
ide furnishes oxygen 
which converts sihcon, 
sulphur, and phosphorus 
into oxides (acid oxides), 




Fig. ii)i. — Drawing a sample of steel 
from an open-hearth furnace for a 
chemical test 



which form a slag with the hearth Hning (a basic oxide). 
The charge is heated from six to twelve hours. Sam- 
ples are drawn out at intervals (Fig. 181) and tested 
by the chemist. When tests show that the metal contains 

the desired propor- 
tion of carbon and 
other constituents, 
the steel is tapped 
into ladles, and cer- 
tain materials are 
added to improve 
the product, e.g. 
aluminium or sih- 
con (or ferro-sih- 
ron) , which removes 
oxygen, and ferro- 
manganese (Fig. 
182). It is then 

Fig. 182. - Tapping an open-hearth furnace quickly pourcd into 




404 



PRACTICAL CHEMISTRY 




molds and allowed to 
cool into ingots (Fig. 
177, middle). Subse- 
quently the ingots are 
softened by reheating 
and rolled, pressed, or 
stamped into desired 
shapes (Figs. 183, 
184, 185). 

The open-hearth 
process is easily con- 
trolled and yields a 
tough, elastic steel, 

Fig. 183. -Making a steel rail -first stage ^^^^^^ -^ excellent for 
bridges, rails, large machines, large guns, and gun carriages. 
496. The crucible process consists in melting wrought 
iron, or low carbon steel, in crucibles made of graphite 
and clay. The charge varies with the product desired. 
For example, iron oxide may be added, or certain 
metals, such as chro- 
mium, vanadium, 
or molybdenum. 
The crucibles are cov- 
ered and then heated 
to a high temperature 
from four to five hours. 
During the melting 
the iron is slowly 
changed into steel by 
absorbing the proper 
proportions of car- 
bon. Crucible steel is 

very hard, and is used Fig. 184. — Making a steel rail — final stage 




IRON AND STEEL 



405 




iS: 



Steel plate passing through 
the last rolling machine 



to make tools, springs, 
drills, dies, pens, and 
needles. 

497. The electric process 

consists in hciUing a selected 
charge of cast iron, or steel 
made from inferior materials, 
in an electric furnace (Fig. 
186). The heat is gen- 
crated, usually, by the arc 
established between the car- 
bon electrode and the melted 
charge. \>ry high temper- 
atures are obtained. More- 
over, the operation is con- 
ducted in a non-oxidizing atmosphere. Hence, the electric process 
is advantageously used in conjunction with the Bessemer and open- 
hearth processes to produce a superior steel free from gases and sul- 
phur. 

498. Properties of steel. — The properties are numerous 
because there are many kinds of steel. Thus, steel, using 
this term broadly, is fusible and malleable, and can be 
forged, welded, and cast. Varieties containing 0.2 per cent 

of carbon are much Hke 
wrought iron and are 
called soft or mild steel. 
Structural steel con- 
tains more carbon (0.2 
to 0.8 per cent) and is 
hard like cast iron, while 
tool steel, which con- 
tains upwards of 1.5 
per cent of carbon, is 
very hard indeed. 

The properties of steel 




Fig. 186. — Sketch of an electric fur- 
nace for the manufacture of steel 



40 6 



PRACTICAL CHEMISTRY 



depend not only on the proportion of carbon (and other 
elements) but also on the special heat treatment which it 
receives. If steel is heated very hot and then suddenly 
cooled by plunging it into cold water or oil, it becomes 
brittle and very hard (Fig. 187). But if heated and 
cooled slowly, it becomes soft, tough, and elastic. 





All 



Fig. 187. — Photomicrographs of hard steel (right) and cast steel (left) 
(Compare Fig. 175) 



grades of hardness can be obtained between these two 
extremes. Thus, if hardened steel is reheated to a definite 
temperature, determined approximately by the color the 
oxidized metal assumes, and then properly cooled, a de- 
sired degree of hardness and elasticity is obtained. This 
last operation is called tempering. 

499. Special steels, or steel alloys as they are sometimes 
called, are made by introducing certain metals, or their 
alloys with iron, into steel produced by the open-hearth 
or crucible process. These special steels have properties 
which adapt them to indispensable uses. Nickel steel 
up to 3.5 per cent nickel is hard and tough, and is used for 
armor plate, cables, drills, and marine engine parts. Steel 
containing 36 per cent of nickel expands so very slightly 



IRON AND STEEL 407 

with changes of temperature that it is made into surveyor's 
tapes, pendulums, and scientific apparatus. It is called 
invar. The alloy containing about 42 per cent of nickel 
expands and contracts to the same extent as platinum and 
glass. It is used in making wire glass and as the wire that 
connects the inner and outer parts of electric light bulbs. 
It is called platinite and is used instead of the scarce and 
expensive metal platinum. 

Chromium steels, made by adding the alloy ferro-chrome 
to molten steel, seldom contain more than 2 per cent of 
chromium. They are very hard and are used for armor- 
piercing projectiles, safes, and crushing machinery. If 
small proportions of other metals are added, such as vana- 
dium and manganese, the steels are tough, elastic, and 
hard ; they resist shocks and strain, and are used in making 
automobile parts. Tungsten steels are hard, and if of the 
right composition, do not lose their hardness at a red heat. 
A typical one contains 18 per cent of tungsten, 3.5 per cent 
of chromium and a small fraction of a per cent of vanadium. 
They are called high speed steel and are used to make tools 
for cutting metals ; the tools, unlike the usual tool, will cut 
when they are dull red from the heat produced by friction. 
Molybdenum sometimes replaces tungsten, and much less 
is needed to produce the same results as with tungsten. 
Manganese steels, containing about 13 per cent of manga- 
nese, are extremely hard without being brittle. They are 
used for making the jaws of rock-crushing machinery, 
dredger buckets, safes, parts of brakes, and rails. 

Vanadium is often added in small amounts to special 
steels to increase certain desired properties. 

500. Preparation and properties of pure iron. — Chemically pure 
iron, though uncommon in commerce, can be obtained as a powder 
by reducing the oxide with h}'drogen (" iron by hydrogen ") or 



4o8 PRACTICAL CHEMISTRY 

as irregular plates by the electrolysis of a solution of ferrous sul- 
phate. 

Pure iron is a silvery white, lustrous metal. It is ductile and 
malleable, and softer than ordinary iron, being about as soft as alu- 
minum. The specific gravity is 7.86 and the melting point is 1520° 
C. It is attracted by a magnet, but soon loses its own magnetism. 

Iron forms an oxide (Fe304), if heated to a high temperature in 
steam or burned in oxygen. Iron readily interacts with dilute acids, 
and as a rule hydrogen and ferrous compounds (e.g. ferrous sulphate, 
FeS04) are the products. 

501. What is iron rust ? — Dry air has no effect on iron, but moist 
air rusts it. Rusting is a complex process and is explained in different 
ways. A recent and acceptable interpretation based on the theory of 
ionization is as follows : The iron goes into solution as ferrous ions 
(Fe+"^). Hydrogen ions (H+) from the water lose their charges and 
become atoms ; the atoms unite to form molecules which escape as 
hydrogen gas (H2). The ferrous ions combine with the h3Tlroxyl 
ions (0H~) left in the water, thereby forming ferrous hydrox- 
ide (Fe(OH)o), which is subsequently converted into the complex 
substance called iron rust. Once begim, rusting proceeds rapidl}^ 
because the film of rust is not compact enough to protect the metal. 

502. Two series of iron compounds. — Iron forms two 
series of compounds — ferrous and ferric. Corresponding 
members differ in properties. In each series the iron 
plays a different role. We sometimes distinguish the 
members of the two series by saying the valence of iron is 
two in ferrous compounds and three in ferric. We also 
distinguish the two series by saying ferrous salts in so- 
lution give ferrous ions (Fe++) and ferric salts give ferric 
ions (Fe+++). 

Ferrous comipounds pass readily into the corresponding 
ferric compounds by oxidation. For ex2imp\e, ferrous chlo- 
ride in hydrochloric acid solution becomes ferric chloride 
in the presence of an oxidizing agent, such as nascent oxy- 
gen, hydrogen peroxide, nitric acid, or potassium perman- 
ganate. An equation is : — 



IRON AND STEEL 409 

2FeClo + 2HCI + O = 2ECCI3 + H.2O 

Ferrous Hydrochloric Oxygen Ferric Water 

Chloride Acid (Nascent) Chloride 

Whereas ferric chloride becomes ferrous chloride by the 
action of a reducing agent, e.g. nascent hydrogen, hydrogen 
sulphide, sulphurous acid, or stannous chloride (SnCl2)- 
An equation is : — 

FeCls + H = FeClo + HCl 

Ferric Hydrogen Ferrous Hydrochloric 

Chloride (Xascent) Chloride Acid 

In these two reactions it is unnecessary to use nascent 
oxygen or hydrogen. Thus, ferrous chloride becomes 
ferric chloride by action with chlorine, while ferric 
chloride becomes ferrous chloride by action with iron^ 
thus : — 

2FeCl2 + CI2 = 2FeCl3 and 2FeCl3 + Fe = sFeCls 

That is to say, the change from a ferrous to a ferric compound 
is the same as the change from sulphurous acid to sulphuric 
acid. It is an example of oxidation, while the reverse is 
reduction. To be sure, no ox\^gen is involved. Never- 
theless, we often use the terms oxidation and reduction in a 
broader sense than mere addition and removal of the element 
oxygen (23, 24, 43, 55). 

Let us interpret the broader meaning of these terms. Oxygen 
belongs to the class of negative elements. So does chlorine. Xow 
if we add chlorine to ferrous chloride, we are doing chemically just 
what we do if we add oxygen to sulphurous acid, viz. oxidizing. In 
a broad sense, then, oxidation is the process of adding oxygen, chlorine, 
or another negative element. Conversely, reduction is the process 
of removing oxygen, chlorine, or another negative element. 

As stated above, the valence of iron is two in ferrous and three 
in ferric compounds. In passing from ferrous to ferric compounds 
the valence of the iron increases; and conversely, from ferric to 



4IO PRACTICAL CHEMISTRY 

ferrous it decreases. From the standpoint of valence, oxidation is 
an increase in the valence of a positive element {i.e. a metal), whereas 
redaction is a decrease. 

Furthermore, since dissolved iron salts pass readily from one series 
to the corresponding members of the other, oxidation is sometimes 
called adding positive electricity, e.g. Fe++ to Fe+++ ; whereas re- 
duction is the removal, e.g. Fe+++ to Fe'^+ 

503. Three oxides of iron. — Iron forms three oxides. 
Ferrous oxide (FeO) is an unstable black powder — an 
unimportant compound. Ferric oxide (Fe203) occurs 
native as hematite. This oxide is manufactured by heating 
the ferric hydroxide (Fe(0H)3) obtained as a by-product 
in the cleaning of iron castings, rods, and sheets. One 
variety, called rouge or crocus, is used to pohsh glass and 
jewelry. Another variety, called Venetian red, is used to 
make red paint. Ferrous-ferric or ferroso-ferric oxide 
(magnetic oxide of iron, Fe304) occurs as magnetite; if 
magnetic, it is called loadstone. It is produced as a black 
film or scale by heating iron in the air ; heaps of it are often 
seen beside the anvil in a blacksmith's shop. The firm 
coating of this oxide formed by exposing iron to steam pro- 
tects the metal from further oxidation ; iron thus coated is 
called Russia iron. Some authorities regard this oxide as 
iron ferrite (Fe(Fe02)2)- 

504. Iron hydroxides. — Ferrous hydroxide (Fe(0H)2) 
is a white soUd formed by the interaction of a ferrous salt 
and an hydroxide. Exposed to the air, it soon turns green, 
and finally brown, owing to oxidation to ferric hydroxide. 
Ferric hydroxide (Fe(0H)3) is a reddish brown soHd, formed 
by the interaction of a ferric salt and an hydroxide, 
thus : — 

FeCla + sNaOH = Fe(0H)3 + sNaCl 

Ferric Sodium Ferric Sodium 

Chloride Hydro.xide Hydroxide Chloride 



IRON AND STEEL 411 

505. Ferrous sulphate (FeS04) is a green salt obtained 
by the interaction of iron (or of ferrous sulphide) and dilute 
sulphuric acid. It is manufactured by roasting (i.e. oxi- 
dizing iron pyrites (FeSo), or by exposing pyrites to moist 
air ; the mass is extracted with v/ater containing scrap iron 
and a Httle sulphuric acid. The large light green crystals 
(FeS04.7H20) are called green vitriol or copperas. 

Exposed to air, ferrous sulphate effloresces and oxidizes. 
Hence the ferrous sulphate used to prepare a ferrous solu- 
tion, e.g. in testing for nitric acid or a nitrate, 190, should 
be thoroughly washed to remove the ferric salt. 

Large quantities are used in dyeing silk and wool, as a 
disinfectant, and in manufacturing ink, bluing, and pig- 
ments. Much black writing ink is made essentially by 
mixing ferrous sulphate, nutgalls, gum, and water. A 
mixture of ferrous sulphate and lime is used to purify water 
and sewage by the settling process (69). 

506. Iron sulphides. — Commercial ferrous sulphide (FeS) is a 
black, brittle, metallic-looking solid made on a large scale by fusing 
a mixture of iron and sulphur. It is also obtained as a black pre- 
cipitate by the interaction of a dissolved ferrous salt and ammo- 
nium sulphide. It is used chiefly in preparing hydrogen sulphide 
(255). 

One of the commonest minerals is ferric sulphide (iron disulphide, 
iron pyrites, pyrite, FeSo). It is a lustrous, brass-yellow solid. 
Crystals of pyrites are often mistaken for gold — hence the name 
" fool's gold." It is valueless as an iron ore, but large quantities are 
used in making sulphuric acid. 

507. Iron chlorides. — When iron interacts with hydrochloric 
acid, ferrous chloride (FeCl2) is formed in solution. Heated in the 
air or with potassium chlorate or nitric acid, it is changed into ferric 
chloride. (For the equation see 502, second paragraph.) Ferric 
chloride (FeClg) is a deliquescent solid. It is prepared by passing 
chlorine into ferrous chloride solution, or by the interaction of iron and 
aqua regia. With nascent hydrogen or another reducing agent, 



412 PRACTICAL CHEMISTRY 

ferric chloride becomes ferrous chloride. (See 502, second paragraph ) 
Ferric chloride solution is acid, owing to h3^drolysis (452). 

508. Ferrocyanides and ferricyanides. — The most im- 
portant is potassium ferrocyanide (K4Fe(CN)6). It is a 
lemon-yellow, crystallized solid, containing three mole- 
cules of water of crystallization, and is sometimes called 
yellow prussiate of potash. Unlike the simple cyanogen 
compounds {e.g. HCN and KCN), it is not poisonous. It is 
manufactured by fusing iron filings with potassium carbon- 
ate and nitrogenous animal matter (such as horn, hair, 
blood, feathers, and leather). The mass is extracted with 
water, and the salt is separated by crystallization. Large 
quantities are used in dyeing and calico printing, and in 
making bluing and potassium-cyanogen compounds. Po- 
tassium ferricyanide (K3Fe(CN)6) is a dark red crystallized 
solid, containing no water of crystallization. It is often 
called red prussiate of potash. It is manufactured by oxi- 
dizing potassium ferrocyanide. In alkaline solution it is a 
vigorous oxidizing agent, and finds extensive use in dyeing. 

509. Making a blue print. — Blue print paper is prepared by coat- 
ing paper with a mixture of potassium ferricyanide and ammonium 
ferric citrate solutions, and drying in a dark place. In the sunlight 
the ferric salt is partly reduced and forms a bronze colored deposit 
by interaction with the potassium ferricyanide. . 

If such prepared paper is covered with a photographic negative, 
or with transparent cloth marked with lines in black ink, and placed 
in the sunlight, the paper is acted upon only in the exposed places. 
Upon washing, the exposed parts become blue, and the covered parts 
white. 

510. Tests for ferrous and ferric compounds. — Ferrous 
salts and potassium ferricyanide interact in solution and 
precipitate ferrous ferricyanide (Fe3(Fe(CN)6)2)- This is 
a dark blue solid, and is called TurnbuU's blue. Ferric 
salts interact with potassium ferrocyanide and precipitate 



IRON AND STEEL 413 

ferric ferrocyanide (Fe4(Fc(CN)6)3)- This precipitate is 
likewise a dark blue solid, and is called Prussian blue. 
By these tests ferrous and ferric salts can be distinguished. 
Hence to test for — 

Ferrous salts add potassium ferricyanide, 
Ferric salts add potassium ferrocyanide. 

In each test we obtain a dark blue precipitate, but only if 
we use " ferrous with ferri- " and " ferric with ferro- ." 

Since these two results are apt to confuse, let us interpret them. 
Ferrous salts in solution form ferrous ions (Fe"^"^). Potassium ferri- 
cyanide in solution forms potassium ions (K+) and ferricyanide ions 
(Fe(CN)6 ). When ferrous chloride and potassium ferricyanide 
solutions are mixed, ferrous ions unite with ferricyanide ions and form 
ferrous ferricyanide, thus : — 

3Fe++ + 6C1- + 6K" + 2Fe(CN)6--- = Fe3(Fe(CN)6)2 -f 60" + 6K" 

Ferrous Ferricyanide 

Similarly, ferric chloride and potassium ferrocyanide react thus : — 
4Fe+++ + 12CI- + 12K+ + 3Fe(CN)6 = 

Fe4(Fe(CN)6)3 + 12CI- + 12K+ 
Ferric Ferrocyanide 

The dark blue precipitate is formed only by the combination of either 
ferrous and ferricyanide ions or ferric and ferrocyanide ions. 

Besides the above tests for ferric salts, potassium sulpho- 
cyanate (KCNS) produces a red solution or ferric sulpho- 
cyanate (Fe(CNS)3) with ferric salts, but leaves ferrous 
salts unchanged. 

EXERCISES 

1. Name the ores of iron. What proportion of the earth's crust 
is iron? Compare with the abundance of other elements. 

2. Describe a blast furnace. 

3. Describe the manufacture of cast iron. 

4. Apply Exercise 3 to wrought iron. 

5. State the characteristic properties of cast iron and wrought iron. 

6. Describe the manufacture of steel by {a) the Bessemer process, 
{b) the open-hearth process, and (c) the crucible process. 



414 PRACTICAL CHEMISTRY 

7. Compare the composition of cast iron, wrought iron, and steel. 

8. Study topics: (a) Production and transportation of iron ore. 
(b) Uses of steel, (r) Meteorites, (d) Primitive iron smelting. 
(e) Armor plate, (f) Special steels, (g) Iron objects in the school 
building. (//) Iron in the home. (/) Tests for iron. 

9. What is copperas, rouge, crocus, iron pyrites, green vitriol, 
hematite, magnetite, yellow prussiate of potash? 

10. How are ferrous changed into ferric compounds, and vice versa? 
Give equations. 

11. Practical topics: (a) Cite proofs that iron is widely distributed. 

(b) How would you test coal ashes for iron? (c) How would you 
prove by experiment that bluing contains an iron compound? 

12. Sketch from memory (a) a blast furnace, (b) a converter in 
operation, (c) an open-hearth furnace. 

13. Starting with iron, how would j^ou prepare in succession ferrous 
chloride, FeCls, ferric hydroxide, ferric chloride, Fe4(Fe(CX)6)3? 

14. Review these topics by iron compounds : (a) Law of multiple 
proportions. (See Problem 3.) (b) Oxidation and reduction (502), 

(c) Valence (502). (d) Hydrolysis (452). 

15. Solutions of ferrous sulphate sometimes give a test for ferric 
iron. Why? 

PROBLEMS 

1. Calculate the weight of iron in (a) 70 tons of copperas, {b) 3 tons 
of hematite (95 per cent pure), (c) 2 kg. of pyrite, (d) 1000 lb. 
of magnetite. 

2. Write the formulas of (a) the ferrous and (6) the ferric salts of 
the following acids : Hydrobromic, hydriodic, carbonic, nitric, ortho- 
phosphoric. 

3. Calculate the percentage composition of (a) the three oxides and 

(b) the two chlorides of iron, and show how the two sets of compounds 
illustrate the law of multiple proportions. 

4. Calculate the following: (a) the weight of ferrous carbonate 
needed to produce 25 1. of CO2 (standard conditions) ; {b) the weight 
of iron formed by the interaction of hydrogen and 220 gm. of Fe304; 

(c) the weight of pure iron that can be made from 1000 tons of iron ore 
(94 per cent hematite). 

5. Complete and balance the following : (a) FeCb + (NH4)2S = 

FeS H '-; (b) FeCl3 + = Fe(0H)3 + NH4CI; (r) Fe + 

= Fe,03; (d) K3Fe(CX)6+ = + K2SO4; (e) K4Fe(CX)6 

+ = + KCl. 

6. What is the simplest formula of a compound, if 9 gm. of it 
yielded 4.8 gm. of sulphur and the rest iron? 



CHAPTER XXXII 



ALUMINIUM AND ITS COMPOUNDS 
— CLAY AND CLAY PRODUCTS 

511. Occurrence. — Aluminium (often called aluminum) 
compounds are numerous, abundant, and widely dis- 
tributed. About 8 per cent of the earth's crust is com- 
bined aluminium ; in abundance it ranks first among the 
metals and third among the elements (11). All important 
rocks except limestone and sandstone contain aluminium 
silicates and other metals. Clay is also aluminium sihcate. 
Corundum and emery are impure aluminium oxide (AI2O3). 
Bauxite is an aluminium hydroxide (H4AI2O5) ; it is often 
colored red by iron oxide. CryoUte is sodium aluminium 
fluoride (NagAlFe) ; it is a white icelike soUd. 

512. Manufacture of aluminium. — Aluminium is manu- 
factured by the electrolysis of aluminium oxide (AI2O3). 
The purified oxide, which 
is prepared from bauxite, 
is dissolved in melted cryo- 
Ute, and when the current 
passes, aluminium is depos- 
ited at the cathode. This 
process was discovered in 
1886 by the American chem- 
ist Hall and perfected by 
him. Fig. 188. — Sketch of the appara- 
tus for the manufacture of alu- 

A sketch of the apparatus is minium by the electrolysis of alu- 
shownin Fig. 188. An open iron minium oxide 

415 




41 6 PRACTICAL CHEMISTRY 

vessel (C, C) lined with carbon is the cathode. Connection with the 
cathode is made at D. The anode consists of several graphite bars 
{A, A, etc.) attached to a copper rod {R), which can be lowered as 
the graphite is consumed (by the liberated oxygen) . 

The bottom of the box is first covered with cryoHte, the anode is 
lowered, and the box is then filled with cryolite (to which some calcium 
fluoride is added to reduce the melting point). The current is turned 
on, and the resistance generates enough heat to melt the cryolite. 
Pure, dry aluminium oxide is now added, which dissolves in the cryo- 
lite and doubtless dissociates somewhat as electrolytes do in water. 
The oxygen goes to the anode and unites with the carbon. The 
graphite anodes have to be replaced. 

The aluminium is liberated at the cathode, sinks through the 
cryolite, and collects as a liquid at the bottom of the vessel. The 
process is continuous, fresh aluminium oxide being added and the 
molten aluminium being drawn off at intervals. The cryolite is not 
decomposed as long as aluminium oxide is present. 

513. Properties. — Aluminium is a lustrous white metal. 
It is very light in weight, being in fact the Hghtest of the 
common metals. Its specific gravity is only about 2.6 
while that of iron is 7.8. It is ductile and malleable, and 
is extensively made into wire and sheets. It is a good con- 
ductor of heat and electricity. Compared with most 
metals aluminium is rather hard and strong. It melts at 
about 658° C. 

Aluminium in the semi-molten state can readily be ex- 
truded, i.e. forced or pressed out through an opening into 
desired shapes. Just below the melting point it is brittle 
and can be ground into powder. Aluminium can be cast 
and welded, though it cannot be turned well in a lathe, nor 
can it be readily soldered to produce a permanent joint. 

514. Chemical conduct. — Aluminium is only very 
sHghtly tarnished by air, owing to the protecting film of 
oxide that forms on the surface. It combines vigorously 
with oxygen at high temperatures. It is a powerful re- 



ALUMINIUM AND ITS COMPOUNDS 417 

ducing agent (517). Hydrochloric acid reacts readily with 
it, thus : — 

2AI + 6HC1 = 2AICI3 + 3H2 

Aluminium Hydrochloric Acid Aluminium Chloride Hydrogen 

Under ordinary conditions nitric and dilute sulphuric acids 
do not affect it ; concentrated sulphuric acid acts upon it, 
forming aluminium sulphate. Sodium chloride interacts 
with it, if dilute acids are present. With sodium and potas- 
sium hydroxides it forms aluminates and hydrogen, thus : — 

6XaOH + 2AI = 2Xa3A103 + 3H2 

Sodium Hydroxide Aluminium Sodium Aluminate Hydrogen 

515. Uses. — The varied properties of aluminium, 
especially its strength, hghtness, and durabiUty, adapt it 
to numerous uses, e.g. parts of military outfits, caps for 
jars, surgical instruments, tubes, fittings of boats, auto- 
mobiles, and airships, parts of opera glasses and telescopes, 
framework of cameras, stock patterns for foundry work, 
hardware samples, and scientific apparatus. Varied forms 
of aluminium cooking utensils have become very popular. 

Its attractive appearance leads to its extensive use as an 
ornamental metal, both in interior decorative work and in 
numerous small objects. Aluminium leaf is used for letter- 
ing book covers and signs, and the foil has largely replaced 
tin as a wrapper for food and candy. The powder sus- 
pended in an adhesive liquid is used as a paint for steam 
pipes, radiators, smokestacks, and other metal objects 
exposed to heat or the weather. Aluminium wire is used 
to some extent as a conductor of electricity. 

Large quantities of aluminium are consumed in deoxidizing steel, 
i.e. removing air bubbles from the molten steel, thereby preventing 
the formation of small holes in the castings (494, 495). 



4i8 PRACTICAL CHEMISTRY 

516. Alloys. — Aluminium forms alloys with copper. The pro- 
portions of aluminium vary widely (from 5 to 95 per cent) thus giving 
a great variety of useful alloys. Those containing from 5 to 10 per 
cent of aluminium are called aluminium bronze ; they are yellow and 
are used in making jewelry and statuary. Whereas those containing 
90 to 95 per cent of aluminium are silver-white ; these alloys are 
used in making castings and household ware, and are called duralumin. 

An alloy wath magnesium, called magnalium, contains from 75 
to 90 per cent of aluminium. It is hard, light, attractive, and durable, 
and is used as parts of chemical balances and scientific instruments. 

517. Thermit. — - Aluminium is a powerful reducing 
agent. This property is utilized in the manufacture of cer- 
tain metals and in welding. When a mixture of chromium 
oxide and powdered aluminium is ignited at one point, 
the reduction proceeds rapidly throughout the mixture and 
the intense heat fuses the chromium, which can be removed 
from the crucible in a lump ; the aluminium oxide rises to 
the top of the metal as a slag. The equation is : — 



Cr203 + 2AI 


= 2Cr 


+ AI2O3 


Chromium Oxide Aluminium 


Chromium 


Aluminium Oxide 



Other metals, e.g. manganese, hitherto rare or expensive 
are similarly prepared. 

If a mixture of ferric oxide (Fe203) and powdered alu- 
minium is ignited, molten iron at a temperature of about 
3000° C. is produced. By using a special form of apparatus 
the molten iron can be conducted from the crucible into a 
mold around a joint or fracture (Fig. 189, right). This 
method is widely used to weld steel rails and repair frac- 
tures in machinery (Fig. 190). 

Mixtures of aluminium and oxides, used for this purpose, 
are called thermit, and the method is known as the alumino- 
thermic method. 

518. Aluminium oxide (AI2O3) is the only oxide of alu- 



ALUMINIUM AND ITS COMPOUNDS 



419 



minium. It is often called alumina, as silicon dioxide is 
called silica. Its native forms are corundum and emery. 




Fig. 189. — Welding a steel rail with thermit. Sketch of the crucible 
and mold in position (right). The operation is shown on the left 



Both are very hard substances, pure corundum ranking 
next to diamond. The transparent varieties of corundum 
have long been prized as gems, among them being the 




Fig. 190. — A crankshaft repaired by the thermit process 

sapphire and ruby. Emery was formerly used as an ab- 
rasive. But it has been largely replaced by an artificial 



420 PRACTICAL CHEMISTRY 

oxide called alundum. This product is manufactured by 
heating more or less pure alumina in an electric furnace. 
On cooling, the mass forms a hard soHd like corundum. 

When alumina or any other compound of aluminium is heated on 
charcoal with a blowpipe, then cooled, moistened with cobaltous ni- 
trate solution, and heated again, the mass turns a beautiful blue 
color. This is a test for aluminium. 

519. Aluminium hydroxide (A1(0H)3) is a white, jelly- 
Kke solid formed by adding ammonium hydroxide to a so- 
lution of aluminium salt, thus : — 

AICI3 + 3NH4OH = A1(0H)3 + 3NH4CI 

Aluminium Ammonium Aluminium Ammonium 
Chloride Hydroxide Hydroxide Chloride 

It is insoluble in water, but it dissolves in strong acids and 
strong bases (in excess), forming respectively aluminium 
salts and aluminates. 

In aluminium hydroxide, aluminium acts either as a metal or a 
non-metal (397), that is, aluminium hydroxide has basic and acid 
properties, though both are weak. An equation illustrating the 
basic property is : — 

A1(0H)3 + 3HCI = AICI3 + 3H2O 

Aluminium Hydrojdde Hydrochloric Acid Aluminium Chloride Water 

One illustrating the acid property is : — 

A1(0H)3 + sNaOH = NasAlOs + 3H2O 

Aluminium Hydroxide Sodium Hydroxide Sodium Aluminate 

520. Aluminium sulphate (AI2 (804)3) is a white solid 
prepared from clay or bauxite by heating with sulphuric 
acid. The crystallized salt usually has the formula 
AI2 (504)3 -181120. It is used in dyeing and paper making, 
in purifying water, in making white leather, and in making 
alum and other aluminium compounds. 



ALUMINIUM AND ITS COMPOUNDS 



421 



A solution of iiluminium sulphate has an acid reaction on account of 
hydrolysis (452) ; the equation for the hydrolysis is : — 



A1,(S0,)3 


+ 


6H,0 = 


= 2A1(0H)3 


+ 


3H-..S04 


Aluminium 




Water 


Aluminium 




Sulphuric 


Sulphate 






Hydroxide 




Acid 



Practical application is made of this reaction in purifying water. 
Upon adding aluminium sulphate and lime to impure water, the gelat- 
inous aluminium hydroxide that is precipitated slowly settles and 
carries with it suspended particles and bacteria (69). 

521. Alums. — A mixture of concentrated solutions of 
aluminium sulphate and potassium sulphate deposits 
crystals of potassium alum or. simply alum (Fig. 191). 
Its formula is K2Al2(S04)4 or K2SO4.AI2 (804)3. It is the 
type of a class of similar salts called alums, which can be 
prepared from sulphates of univalent and trivalent metals 
{e.g. K, Na, NH4, and Al, Cr, Fe). 
For example, chrome (or chro- 
mium) alum is K2S04.Cr2(S04)3. 

Alums are rather soluble in 
water, and their solutions have an 
acid reaction owing to hydrolysis 
(452, 520). They crystallize as 
octahedrons and contain twenty- 
four molecules of water of crystal- 
lization (Fig. 191). When heated, 
alums lose their water of crystalH- 
zation and usually some sulphur 
trioxide. and become a white 




Fig. 191. — Alum crystals 
deposited from a concen- 
trated solution 



powder or a porous mass known as burnt alum. 

Alum (and sometimes aluminium sulphate) is an ingredient of 
alum baking powders (454) ; the acid needed to liberate carbon 
dioxide is formed by the hydrolysis of the alum. 

Alums are used in dyeing and printing cloth, in tanning and paper 
making, as a medicine, for hardening plaster, in making wood and 



422 PRACTICAL CHEMISTRY 

cloth fireproof, and in preparing aluminium compounds. Aluminium 
sulphate is displacing aluminium alums for many purposes, especially 
the purification of water. 

522. Mordants. — Aluminium hydroxide is extensively 
used as a mordant in dyeing. Many dyes must be fixed 
in the fiber by a metalUc substance, otherwise the color 
would be easily removed. 

The cloth to be dyed or printed is first impregnated or printed with 
an aluminium salt, such as aluminium acetate, and then exposed to 
steam or treated with aluminium hydroxide. This operation changes 
the aluminium salt into aluminium hydroxide, which is precipitated 
in the fiber of the cloth. The mordanted cloth is next passed through 
a vat containing a solution of the dye, which unites chemically or 
mechanically (perhaps both) with the aluminium hydroxide, forming 
a colored compound. The latter is relatively insoluble and cannot 
be easily washed from the cloth, i.e. it is a fast color. 

523. Clay is the most common and perhaps the most 
useful compound of aluminium. It is a more or less im- 
pure aluminium siUcate, formed by the slow decomposition 
of rocks containing aluminium compounds, especially the 
feldspars (386). Pure, typical feldspar is potassium alu- 
minium siHcate (KAlSiaOg) • The products of its decomposi- 
tion are chiefly an insoluble aluminium siHcate and a soluble 
alkaline siUcate. The latter is washed away. The pure 
aluminium siHcate which remains is kaolin (HiAloSioOg or 
H2Al2(Si04)2.H20). Usually kaoHn is mixed with particles 
of mica and quartz, calcium and magnesium carbonates, 
and iron compounds — the last giving the colors. This 
mixture, which varies in composition, is known as clay. 

All grades of wet clay are plastic and can be molded into various 
objects which retain their shape when dry ; if heated, the dried clay 
does not melt (except at a very high temperature) but becomes a per- 
manently hard mass. These two properties (plasticity when wet and 



ALUMINIUM AND ITS COMPOUNDS 423 

hardness when heated) have been utiUzed for ages in making useful 
and ornamental objects. 

524. Clay products. — ■ Porcelain and china are made by 
mixing kaolin, fine sand, and powdered feldspar, shaping 
the mass into the desired form by molds or on a potter's 
wheel, and then heating in a kiln to a high temperature 
(Fig. 192). The mass when cool is hard and translucent 




Fig. 192. — Scene in the largest chemical porcelain works in the 
United States. Putting porcelain dishes in clay boxes preparatory 
to heating in the kiln 

(if thin), but porous. To be serviceable its surface must be 
glazed. This is done by dipping it into a creamlike mixture 
of feldspar and siUca, similar to that used for making the 
porcelain but more easily fused, and then heating it again. 
The thin coating melts, runs over the surface, penetrates 
the porous mass and fuses with it to some extent, and 
when cold finally forms a shiny, impervious glaze. 

Porcelain is decorated by mixing colored substances with the glaze 
or by painting designs on the surface with metallic paints or colored 
glass, and then heating again. 



424 PRACTICAL CHEMISTRY 

In making pottery the raw materials are less carefully 
selected and prepared, and not heated to such a high tem- 
perature. The best grades can hardly be distinguished from 
porcelain, but usually pottery is much heavier and thicker. 

If less pure, plastic clay is used and heated to a moderate 
temperature, the product is known as earthenware or stone- 
ware. This is a large class and includes tiles, terracotta, 
jugs, flowerpots, and chemical ware. This ware is porous 
and is sometimes glazed by throwing salt into the kiln just 
before the operation is over. The salt volatilizes and forms 
a fusible sodium aluminium sihcate upon the surface. The 
special grades of stoneware for use in chemical plants are 
made by a more careful procedure. 

Clay products used for construction include bricks, conduits, 
drain pipe, etc. They are made from impure clay and heated just 
enough to harden the mixture. The product varies with the clay, but 
is often colored red owing to iron oxide formed from the iron com- 
pounds in the unburned clay. Buff bricks are made from clay contain- 
ing a small proportion of iron. Fire bricks and other material de- 
signed to withstand high temperatures are made from clay containing 
considerable silica. 

EXERCISES 

1. Prepare a summary of (a) aluminium, (b) the oxide and hydroxide, 
(c) the sulphate and alums. 

2. Describe the manufacture of aluminium. 

3. Discuss the interaction of aluminium hydroxide with acids and 
with alkalies. 

4. Topics for home study : (a) History of aluminium, (b) Ceram- 
ics, (c) Clay, (d) Dyeing with mordants, (e) Uses of alumin- 
ium. (/) Aluminium in gems, (g) Use and care of aluminium ware. 
{h) Hydrolysis of aluminium compounds, (i) Two pans are identical 
in size and thickness of material, one being of aluminium and the other 
of iron. Compare their weights. 

PROBLEMS 

1. Calculate the weight of aluminium in (a) 20 gm. of aluminium 
oxide, (b) 34 gm. of aluminium hydroxide. 



ALUMINIUM AND ITS COMPOUNDS 425 

2. (a) Starting witli aluminium how would you prepare in suc- 
cession AICI3, Al(OH)3, XasAlOa, AICI3, Al(OH)3, 'AI2O3, Al? (b) Cal- 
culate the percentage composition of two of the compounds in (a). 

3. Write the formulas of aluminium nitrate, aluminium bromide, 
aluminium phosphate (ortho), aluminium fluoride, aluminium silicate 
(meta), potassium aluminate. Calculate the per cent of aluminium 
in three of these compounds. 

4. How many pounds of aluminium in a ton of pure kaolin? 

6. What weight of aluminium can be obtained from 100 kilograms 
of bauxite (93 per cent Al(0Hj3) ? 



CHAPTER XXXIII 

COPPER 

525. Introduction. — Copper has been known for ages. 
Domestic utensils and weapons containing copper were 
used before similar objects of iron. The Latin word cuprum 
gives the symbol Cu. 

526. Copper ores. — Copper, both free and combined, 
is an abundant element. Free or native copper, mLxed v/ith 
a hard rock, is found in large quantities in northern 
Michigan on the shores of Lake Superior. Copper sulphide 
ores occur abundantly in Montana and Utah, e.g. chalco- 
cite (CU2S), chalcopyrite (CuFeS2), and bornite (CusFeSs). 
The basic carbonates, malachite (CuC03.Cu(OH)2) and 
azurite (2CuC03.Cu(OH)2) together with the oxide, cuprite 
(CU2O), are mined in /Vrizona. 

527. Metallurgy of copper. — Free copper is easily ex- 
tracted from the ore. The ore is first crushed, next con- 
centrated by grinding and then washing away the rocky 
impurities down an incHned plane and on shaking tables, 
and finally heated until the copper melts and flows to the 
bottom of the furnace. 

Copper carbonate and oxide ores are reduced by heating them with 
coke in a suitable furnace, somewhat as iron is smelted. The general 
chemical change may be represented thus : — 

CuoO + C = 2Cu + CO 

Copper Oxide Carbon Copper Carbon Monoxide 

The metallurgy of copper-sulphur-iron ores is difficult," 
although chemically it only involves the removal of sulphur 
and iron. The result is accomplished by converting the 

426 



COPPER 



427 



sulphur into sulphur dioxide, which escapes as a gas (or is 
made into sulphuric acid), and the iron into ferrous siHcate, 
which is removed as slag. 

528. Metallurgy of copper-sulphur-iron ores. — Let us 
consider six steps in detail by using Fig. 193. 

1. Crushing. The ore is first crushed to the proper size 
— 2 inches or less — in the crusher A . 

2. Concentrating. The crushed ore is next enriched 
by mechanical concentration, i.e. grinding, washing, shak- 




Fig. 193. — Diagram showing the steps in obtaining copper from 
copper-sulphur-iron ores 



ing, settling, and floating. By these operations useless 
parts of the ore are removed ('^sluiced to the dump") 
from the copper minerals, thereby increasing the 3 per cent 
of copper in the original ore to 8 per cent in the concen- 
trated product. By these processes, 95 per cent of the 
copper in the ore is saved, while nearly two thirds of the 
useless part of the ore is discarded. 

By concentration, three general sizes result, viz. (a) The 
coarse concentrate, which goes from the jig {i.e. shaking 
machine) B to the blast furnace M. (See 4 (2).) 



428 PRACTICAL CHEMISTRY 

(/)) The fine concentrate, which, after the grinding in 
C and jigging in D, goes to the roasting furnace {K). 

{c) The very fine concentrate, which is further concen- 
trated by flotation. The ground ore from E passes through 
the deshming cone F on to the table G ; here part goes to 
the roasting furnace (/v). The rest is ground exceedingly 
fine in the mill H and on into the flotation machine (/-/). 
Here a remarkable change occurs. The fine ore particles 
are mixed with water containing a little oil (and sometimes 
sulphuric acid) . Air is beaten into the mixture by vigorous 
agitation. An oily froth is formed to which the copper mineral 
particles stick and float on the top of the mass, whereas the 
rocky particles sink. The water is removed (by a filter — 
not shown) and the concentrate goes to the roasting fur- 
nace {K). 

3. Roasting. The concentrate from the mechanical con- 
centrator D and flotation concentrator /-/ goes to the 
roasting furnace K. This is a cylindrical steel furnace 
lined with fire brick. Here the charge is heated red-hot 
but not melted ; the heat, after the furnace is once started, 
comes from the burning sulphur. By this treatment 
about 80 per cent of the sulphur is removed and part of the 
copper and iron sulphides are changed into oxides. The 
product goes to the reverberatory furnace (L). 

4. Smelting. The product from the roasting furnace K 
is smelted in the reverberatory furnace L ; and the coarse 
concentrate from the jig B is smelted in the blast fur- 
nace M. That is, they are heated with a flux until they 
melt, just as iron is smelted. By this treatment more 
sulphur (as sulphur dioxide) and iron (as slag) are removed, 
and the copper and iron sulphides melt together to form 
copper matte. There are two kinds of furnaces for smelting : 
(i) In the reverberatory furnace L the heat radiated down 



COPPER 429 

upon the hearth fuses the charge (Fig. 174). Most of the 
iron sulphide becomes iron oxide and forms a slag with the 
lime, silica, and alumina (AI2O3) in the charge, while the 
copper sulphide and the remaining iron sulphide m.elt to- 
gether and sink through the slag to the bottom of the mass. 
The slag runs off continually. The matte is tapped off 
periodically and taken to the converter (iV). (2) The 
blast furnace (M) is much like that used in making cast 
iron (Figs. 171, 172), though it is cooled by a constant flow 
of water through jackets w^hich inclose its sides. The 
charge consists of the coarse concentrate (see 2 (a) above), 
hmestone, and coke. Air is blasted through the furnace. 
Much heat is suppHed by the burning sulphur. By this 
treatment 60 per cent of the sulphur is removed and 
most of the iron is changed to an oxide which forms a slag 
with the hmestone in the charge or with the silica and 
alumina purposely left in the concentrate. The copper 
sulphide melts with the rest of the iron sulphide into copper 
matte. The slag and matte are drawn off through water- 
jacketed spouts into settles, where the matte drops through 
the slag — the slag passing on to the dump and the matte 
going to the converter (.Y). 

5. Converting. This is the last stage. Matte from the 
reverberatory and blast furnaces {L and M) is poured into 
the converter — 65 tons to a charge (Fig. 194). The con- 
verter is much hke the kind used in the Bessemer process 
of making steel (Figs. 176, 177). It is lined with magnesia 
brick. Air is blown through the liquid mass. The sulphur 
burns to sulphur dioxide which escapes through the top, 
w^hile the iron forms a slag v/ith the silica and alumina of 
ore added to supply these substances. About five hours is 
needed to burn out the sulphur and " slag the iron." The 
product, which is metallic copper together with a little iron. 



430 



PRACTICAL CHEMISTRY 




A copper converter in action 



sulphur, and slag, goes to the refining-casting furnace (0). 

The chemical changes in the converter may be repre- 
sented thus : — 

(i) 2FeS + 3O2 = 2FeO + 2SO2 

(2) FeO + SiOo = FeSiOa 

(3) 2CU2S + 3O2 = 2CU2O + 2SO2 

(4) CU2S + 2CU2O = 6Cu + SO2 

6. Casting into anodes. The product from the con- 
verter (N) is further purified in the refining-casting furnace 
by blowing air through it and then stirring it with poles 
of green wood to reduce any oxide. When the refining 
is complete, the copper, now 99.25 per cent pure and called 
blister copper, is cast into anodes (Fig. 195). The anodes 
weigh about 500 pounds each. They are sent to the elec- 
trolytic refinery for final purification by electrolysis (529). 

529. Refining of copper by electrolysis. — Since very 
pure copper (at least 99.95 per cent) is needed in electrical 
industries, the blister copper, as it is called, which is pre- 
pared by the process described above, must be further 



COPPER 



431 



purified to remove the last traces of impurities, especially 

arsenic. This is done by electrolysis, and, the refined metal, 

which is exceedingly 

pure (99.98 percent), 

is called electrolytic 

copper. 

The anodes are sus- 
pended in a solution 

of copper sulphate 

and sulphuric acid. 

The cathodes, which 

are made of thin 

sheets of pure copper, 

also dip into the solu- 

tion (Fig. 196.) 

When the current 

passes, copper ions 

(Cu++) migrate to 

the cathode, lose their charges, and are deposited as me- 

taUic copper, thus building up the cathode (Fig. 197). 

x\n equal weight of copper 
dissolves from the anode. 
The impurities drop to the 
bottom of the cell as a 
shme ; from this shme the 
gold and silver that wxre 
in the copper ore are profit- 
ably extracted. 

530. Properties of cop- 
per. — Copper is distin- 
guishable from all other 




Fi£ 



195. — Casting refined copper into 
anodes 



; — MM 



M I M 



.. //////,//////y,//y/.y. .///,/y,. 



Fig. 196. — Sketch of the appara- 
tus for the preparation of pure 
copper by electrolysis. A, A, A 
are anodes, and C, C, C are 
cathodes 



metals by its pecuUar reddish color. It is flexible, duc- 
tile, malleable, and tough. It melts at 1083° C. Its spe- 



432 



PRACTICAL CHEMISTRY 



^" 


'-''IfjMttJIJ^^^^ 


H^ iliU^^ 


m 


^^1 '^^*'*'*i*T'~?3^5^^'*??r'*'^i^yiMl^^B 


MmMm 


feUr 


jWm ^^^^HtlrV 


^m-mili 


^^^ja 


^'fl^^B l^^^^^^^^^^l^H j^ * H^K 


Wmi^ 


iMMC 


tZ^lTtif. ;^^^ 




^!i^"^- — -^\:-*^ 


"1 ''•"w^;*- 


■■- ^^^"'^^^^^^a^; 


>^^^§^ 


fi 




^^— M^fc 


HI 


v'^l^^r^^^^^VflHi^te^ ^^•- 


;^ ^e^^^;:^^^::..- 



Fig. igj. — Removing cathodes of pure copper from a cell in one of the 
rooms of an electrolytic refining plant 

ciiic gravity is 8.9. Copper is an excellent conductor of elec- 
tricity — the best of the cheaper metals. 

Exposed to ordinary air, it turns dull owing to a thin 
film of oxide. In moist air it gradually becomes coated 
with a green basic copper carbonate. Heated in the air, 
it is first changed into black copper oxide (CuO), and at a 
high temperature it colors a flame emerald-green. With 
nitric acid it forms copper nitrate and nitrogen oxides (189, 
194, 195) ; with hot sulphuric acid it yields copper sulphate 
and sulphur dioxide (260). Hydrochloric acid has httle 
eft'ect upon it. 

Copper displaces some metals if suspended in solutions 
of their compounds, e.g. a clean copper wire, if placed in a 
solution of any mercury compound, soon becomes coated 
with mercury ; on the other hand, metals like iron, zinc, 
and magnesium displace copper from its solution, e.g. a 
nail or knife blade soon becomes coated with copper if 
dipped into a solution of any copper compound. Scrap 
iron is often used to precipitate copper on a large scale. 



COPPER 



433 



531. Tests for copper. — (</) The reddish color, pecuHar " cop- 
pery " taste, and green color imparted to a llame serve to identify 
metallic copper, (h) An excess of ammonium hydroxide added to a 
solution of a copper compound produces a beautiful deep blue solu- 
tion, (c) A few drops of acetic acid and potassium ferrocyanide 
solution added to a dilute solution of a copper compound produce a 
brown precipitate of copper ferrocyanide (Cu2Fe(CN)6). 

532. Uses of copper. — Large quantities of copper wire 
are used to conduct electricity, e.g. in operating the tele- 
graph, cable, telephone, electric railway, and electric hght. 
Sheet copper is made into household utensils, boilers, and 
stills, and is also used for roofs and spouts. All nations use 
copper as the chief ingredient of small coins. Much copper 
is utilized in electrical and other apparatus, especially now 
that copper can be cast. Books are printed and illustrated 
from electrotype plates made by depositing copper upon an 
impression of the type or design in wax; in a similar way 
many objects are copper plated (243). Copper is an in- 
gredient of many common and useful alloys, as may be seen 
from the accompanying table. 

Table of Copper Alloys 



NAilE 


Copper 


Zixc 


Alumin- 
ium 


Silver 


Nickel 


Tin 


Aluminium bronze 


90-98 




2-10 








Bell metal . . . 


78 










22 


Brass . . 






63-93 


5-40 










Bronze . . 






60-95 


25 










German silver 






50-60 


25 






20-25 




Gun metal . 






90 










10 


Gold coin . 






10 






Gold 90 






Monel metal 






28 








69 




Nickel coin 






75 








25 




Silver coin . 






10 






90 







533. Two series of copper compounds. — Copper, like 
iron, forms two series of compounds — the cuprous and the 



434 PRACTICAL CHEMISTRY 

cupric. The valence of copper is i in cuprous compounds 
and 2 in cupric. 

Cupric salts are more common. Many are soluble in 
water, and all dilute solutions are blue owing to the presence 
of the blue cupric ion (Cu++). 

Soluble copper compounds are more or less poisonous. Cooking 
utensils made of copper should be used with care. \'egetables, acid 
fruits, and preserves, if boiled in them, should be removed as soon as 
cooked. The vessels themselves should be kept bright to prevent 
the formation of copper salts, which might contaminate the contents, 
Certain lower forms of plant life (algae) are poisoned by copper salts, 
and copper suphate is sometimes added to ponds and reservoirs to 
destroy such growths. 

534. Copper sulphate or cupric sulphate (CUSO4) is a 
blue soHd. It is also called blue vitriol or " blue stone." 
The crystallized salt (CUSO4.5H2O) efSoresces ; heated to 
240° C, all the water escapes, leaving a whitish powder 
called anhydrous copper sulphate. Copper sulphate solu- 
tions have an acid reaction owing to hydrolysis (452) . 

Copper sulphate is used in electric batteries {e.g. the 
gravity cell), in making other copper salts, as a mordant in 
cahco printing and dyeing, and in copper plating and elec- 
trot>^ing. A mixture of copper sulphate and milk of lime, 
called Bordeaux mixture, is sprayed upon trees to kill 
insects. 

Copper sulphate is prepared by treating copper scrap in 
the air with dilute sulphuric acid or by oxidizing copper sul- 
phide. Some of the copper sulphate of commerce is a by- 
product in refining gold and silver with sulphuric acid. 

535. Other copper compounds. — Cuprous oxide (CU2O) is the 
red mineral cuprite. It is precipitated as a reddish powder by heating 
FehHng's solution {i.e. a mixture of solutions of copper sulphate, 
Rochelle salt, and sodium hydroxide) with glucose; its formation 
serves as a test for glucose and sugars like it (345). Cupric oxide 



COPPER 435 

(CuO) is a black solid formed by heating copper in air. It is used to re- 
move sulphur compounds from petroleum. Copper nitrate (CuCXOs);;) 
is a blue, crystallized solid, formed by the interaction of copper and 
dilute nitric acid. It is a cupric salt. It is deliquescent, very soluble 
in water, and is readily decomposed by heat into cupric oxide (CuO) 
and nitrogen oxides. Cupric sulphide (CuS) is the black precipitate 
formed by passing hydrogen sulphide gas into a solution of a cupric 
salt. Malachite is a bright green mineral and is often used as an 
ornamental stone. Azurite is a magnificent blue crystallized mineral. 
Both are basic carbonates and are ores of copper (526). 

536. Displacement of metals. — We have already seen 
that iron, zinc, and other metals displace copper from 
copper salt solutions, and that copper itself displaces mer- 
cury (530). The deposition of metalhc copper and of mer- 
cury are examples of a chemical change in which most metals 
can participate. The displacing relations of metals have 
been carefully studied. It has been found that there is a 
fixed order in which one metal can displace another from 
its solutions. This order is sometimes called the displace- 
ment series. The arrangement of the common metals 
is shown in the accompanying column. 

In this series each free metal displaces succeeding metals 
Displacement Series of from their solutions. For example, zinc 
THE Common :Metals displaces most of the metals in the se- 
Magnesium j.jgg^ while copper displaces only a few. 

.\luminium ^^^^ ^^ interpret a case of displace- 

Zinc ^ , - . , 

j^ ^ ment. In the case of zmc and cop- 

Xin per sulphate solution, not only does 

Lead the zinc displace the copper, but 

Hydrogen the zinc passes into solution. This 

Copper £^^|. ^^^ ^Q shown by testing the 

X ercury solution for zinc. The action (in 

Silver 

Platinum ^^^ ^^^^ ^^ ^^^^ ^^^ copper sulphate 

Gold solution) is represented thus : — 



436 PRACTICAL CHEMISTRY 

Zn + CUSO4 = Cu + ZnSOi 
In the ionic form, this equation is : — 

Zn + Cu++ + SO4-- = Cu + Zn++ + SOr" 

We notice that the essential changes are (i) metallic zinc 
to ionic zinc, and (2) ionic copper to metallic copper. This 
kind of change is sometimes called electrochemical. And 
the displacement series is often called the electrochemical 
series of metals. 

Hydrogen is not a metal in the common acceptance of this term. 
But it is usually included in the displacement series of metals, because 
the metals that precede hydrogen displace it from most acids. That 
is, hydrogen behaves in this respect like other members of the series. 
Recall that hydrogen is like metals in that it forms positive ions (H+) . 

537. The electric cell. — If a rod of zinc and a strip of 
copper are put in a beaker of dilute sulphuric acid, little or 
no action is observed. But if the outer ends are connected 
by a copper wire, bubbles of hydrogen rise from the copper. 
The zinc is slowly " eaten up " but the copper is unchanged. 
The solution will be found, by testing, to contain zinc ions. 
The simultaneous liberation of hydrogen and the disappear- 
ance of zinc mean that metaUic zinc has passed into solu- 
tion as ionic zinc (Zn++) and ionic hydrogen (H+) has come 
out of solution as hydrogen gas (Ho). We might represent 
this action thus : — 

Zn H- 2H+ = Zn++ + Ho 

If the wire is cut and the ends connected with a volt- 
meter, an electric current will be detected flowing from the 
copper strip (positive electrode) through the wire to the 
zinc rod (negative electrode). This means that the elec- 
tric current flows in the solution, by means of ions, from 



COPPER 



437 





the zinc to the copper. This arrangement — zinc, acid, 
copper, — is a simple illustration of an electric cell. The 

electric cell is an example of the trans- ^ 

formation of chemical energy into elec- 
trical energy (Fig. 198). 

All metals have a tendency to pass into so- 
lution, i.e. to become ionic. This tendency 
varies. Any two metals in the displacement 
series may be used with a suitable electrolytic 
solution. The farther apart they are in the 
series, the stronger the current produced. 
Hence the displacement series is also called the 
electromotive series. 



Fig. 198. — Sketch of 
an electric cell 



EXERCISES 

1. Prepare a summary of the metallurgy of copper sulphide ores. 

2. Interpret the electrolytic refining of copper. 

3. State physical properties of copper that fit it for electrical uses. 

4. Give several tests for copper. 

5. Name five alloys of copper. State the uses of three. 

6. What is an electrotype plate ? How is it made? 

7. Topics for home study : (a) Why is the spark from a trolley wire 
often colored green? (b) A tin can will displace copper from copper 
solutions. Why? (c) Nitric acid produces a green-blue stain on a 
silver coin. Why? 

8. Starting with copper, how would you prepare in succession, 
cupric oxide, Cu(N03)2, CuO, Cu, CUSO4, the metal? 

9. Write the formulas of the following compounds by applying the 
principle of valence : Cupric bromide, cuprous chloride, cupric phos- 
phate, cupric sulphate, cuprous iodide. 

PROBLEMS 

1. Calculate the weight of copper in (a) 10 gm. of crystallized copper 
sulphate, (b) i kg. of malachite, and (c) 2000 lb. of chalcocite. 

2. Calculate the percentage composition of the two copper oxides 
and show that they illustrate the law of multiple proportions. (Use 
exact atomic weights.) 

3. Calculate the simplest formulas corresponding to : (a) Cu = 
96.94, H = 3-05; C^) Cu = 57.46, H = 0.91, O = 36.2, C = 5-43- 



438 PRACTICAL CHEMISTRY 

4. How much (o) silver and (b) copper can be obtained from an 
American ten cent coin which weighs 2.44 gm.? 

6. How much CuS can be obtained from 24 gm. of CUSO4? 

6. A flask full of water weighs 153 gm. ; 25 gm. of copper is dropped 
in. The whole now weighs 175.19 gm. Calculate the specific gravity 
of copper. 

7. A certain weight of copper oxide, when heated in a current of hydro- 
gen, lost 59.789 gm. of oxygen and formed 67.282 gm. of water. If the 
atomic weight of oxygen is 16, calculate the atomic weight of copper. 

8. Copper nitrate is heated. What weights of the products are formed 
from 150 gm. of copper nitrate? 



CHAPTER XXXIV 



MAGNESIUM — ZINC — MERCURY 

538. Occurrence of magnesium. — Magnesium is never 
found free. In combination it is widely distributed and 
very abundant, constituting about 2.5 per cent of the 
earth's crust. Dolomite is magnesium calcium carbonate 
(CaMg(C03)2) ; it forms whole mountain ranges in the 
Tyrol and vast deposits in many regions. Dolomite closely 
resembles marble and limestone in its properties, and is 
sometimes called magnesium limestone. Magnesite is mag- 
nesium carbonate (MgCOs) ; it is also abundant. Several 
Stassfurt salts (462) are magnesium compounds, e.g. kainite 
(KCl.MgSO4.H2O) , carnalUte (KCl.MgCl2.6H2O) , and 
kieserite (MgS04.H20). Magnesium is a constituent of 
many rocks and minerals, such as serpentine, talc, 
soapstone, asbestos, and meerschaum ; these are silicates 
(386). The sulphate (MgS04) 
and chloride (MgCl2) are found 
in sea water and in mineral 
springs. 

539. Manufacture of magnesium. 

— Magnesium is manufactured by 
the electrolysis of a fused mixture of 
magnesium chloride and potassium 
chloride obtained from carnaUite. 
An air-tight iron vessel is the cathode 
(Fig. 199). The anode is a carbon 
rod (.4). An inert gas is supplied 
through DD'. The chlorine cs- 

439 



D 



^^^:^rrOr^-> 






B 



Fig. 199. — Sketch of the 
apparatus for the manu- 
facture of magnesium by 
the electrolysis of carnallite 



440 PRACTICAL CHEMISTRY 

capes through E. Magnesium rises to the surface of the fused elec- 
trolyte. 

540. Properties of magnesium. — Magnesium is a lus- 
trous, silvery white metal. It is light, the specific gravity 
being about 1.75. It is tenacious and ductile, and when 
hot can be drawn into wire or rolled into a ribbon, the latter 
being a common commercial form. It is easily kindled by 
a match, melts at 651° C, and can be cast. 

Heated in air, it burns with a dazzling light, producing 
dense white clouds of magnesium oxide (MgO) together with 
a Ht'tle magnesium nitride (MgsNo). It does not tarnish 
in dry air, but in moist air it is soon covered with a film of 
the basic carbonate. It liberates hydrogen from acids. It 
also liberates hydrogen, slowly, from boihng water, thus : — 

Mg + 2H0O = H2 + Mg(0H)2 

When heated in dry nitrogen, it forms magnesium nitride ; 
this property was utiUzed by Ramsay in the separation of 
nitrogen from argon (124, 125). 

Solutions of magnesium salts contain magnesium ions 

(Mg++). 

541. Uses of magnesium. — The light from burning magnesium 
affects a photographic plate, and magnesium powder (mixed with 
potassium chlorate) is used in taking flashhght photographs. It is 
also used in signal lights {e.g. star shells) and fireworks. Magnahum, 
the alloy of magnesium and aluminium, has been described (516). 

542. Magnesium oxide and hydroxide. — Magnesium 
oxide (MgO) is a white, bulky powder. It is formed when 
magnesium burns in the air, but it is manufactured by 
gently heating magnesium carbonate, just as lime is made 
from limestone. It is often called magnesia, or calcined 
magnesia. It combines very slowly with w^ater, forming 
magnesium hydroxide (Mg(0H)2). Like Ume, magnesia 



MAGNESIUM — ZINC — MERCURY 



441 



is infusible and is therefore used in making lire brick, 
crucibles, and furnace linings. It is the main ingredient 




Pipes covered with 



?5 per cent magnesia " to prevent loss of 
heat 



of a mixture used to prevent the loss of heat from steam 
pipes (Figs. 200, 201). 

Magnesium hydroxide is a white solid. It is only very slightly 
soluble in water, and a suspension, called milk of magnesia, is used as 
a medicine to neutralize acidity in the mouth and stomach. 

543. Magnesium sulphate and chloride. — Magnesium 
sulphate (MgS04) is a white soUd. The commercial form 

is often called Epsom 
salts (MgS04.7HoO). It 
is very soluble in water 
and its solution has a 
bitter taste ; it is used 
as a laxative. Magne- 
sium sulphate, like cal- 
cium sulphate, makes water permanently hard (483). 
Magnesium sulphate is used in manufacturing paints, 



•) ) 



Fig 



201. — Section of a pipe showing 
end of protective cover 



442 



PRACTICAL CHEMISTRY 



soap, and sulphates of sodium and potassium, and as a 
coating for cotton cloth. Magnesium chloride (MgCl2) 
is a white soUd. The crystallized salt (MgCl2.6H20) is 
very dehquescent. Magnesium chloride undergoes hy- 
drolysis with hot water, forming magnesium hydroxide 
and hydrochloric acid (452). 

If water containing magnesium chloride {e.g. sea water), is used in 
a boiler, the insoluble magnesium hydroxide forms a hard scale on the 
boiler and the Uberated hydrochloric acid corrodes the metal. Hence 




Fig. 202. — Retorts 



for reduction of zinc oxide (open 
— left) 



risfht, closed 



a hard water containing magnesium chloride (or sulphate) should be 
softened before use (483) . 

544. Other magnesium compounds. — Ammonium magnesium 
phosphate (NH4MgP04) is precipitated when disodium phosphate 
solution and ammonium hydroxide are added to a solution of a mag- 
nesium compound. Its formation serves as a test for magnesium. 
Magnesium carbonate (MgCOs) occurs native as magnesite, and 
combined with calcium carbonate as dolomite. It is extensively used 
as a lining for furnaces {e.g. open-hearth) and converters (494, 495). 
Like the corresponding calcium compound, it forms the soluble acid 
carbonate (MgHo(C03)2) in water containing carbon dioxide (472). 
The commercial salt known as magnesia alba, or simply magnesia, 
is a complex compound (ordinarily Mg(OH)2.3MgC03.3H20). Many 
face powders consist chiefly of magnesia alba. 

545. Occurrence of zinc. — Free zinc is never found. 
The chief ores are zinc sulphide (sphalerite, zinc blende, 
ZnS), and zinc carbonate (smithsonite, ZnCOs). Other 
ores are zinc silicates (calamine, Zn2Si04.H20, willemite, 
Zn2Si04), red zinc oxide (zincite, ZnO), and frankhnite 



MAGNESIUM — ZINC — MERCURY 



443 



(Zn(Fe02)2). Zinc ores are found in Missouri, Kansas, 
and New Jersey. 

546. Metallurgy of zinc. — The ores are usually con- 
centrated (sulphide ore by the flotation process (528, 2 (c))), 
then roasted to form the 
oxide, which is reduced by 
heating with finely pow- 
dered coal. 

The reduction is con- 
ducted in earthenware 
retorts (A) connected 
with double receivers 
(Fig. 202). The retorts 
are heated by gas above 
the boiling point of zinc ; 
so at first the zinc (to- 
gether with some zinc 
oxide) condenses in C as 
a powder called zinc dust 
somewhat as sulphur 
forms flowers of sulphur. 
But when this receiver 
becomes hot, the zinc 

condenses to a liquid in B, from which it is drawn off at 
intervals and cast into bars or plates. The impure zinc 
thus obtained is called spelter. It is freed from carbon, 
lead, iron, cadmium, and arsenic by repeated distillation ; 
very pure zinc is obtained by the electrolysis of a pure 
zinc salt (Fig. 203). 

547. Properties of zinc. — Zinc is a bluish white, lustrous 
metal. At ordinary temperatures it is rather brittle, but 
at 100-150° C. it is soft and can be rolled into sheets and 
drawn into wire ; zinc which has been rolled or drawn does 




Fig. 203. — Lifting the cathodes of 
pure zinc from an electrolytic cell 



444 PRACTICAL CHEMISTRY 

not become brittle on cooling. Above 150^ C. it again 
becomes brittle. It melts at 419° C. If melted zinc is 
poured into water, it forms brittle lumps called granulated 
zinc, which is a convenient form for use in the laboratory. 
Heated in air above its melting point, zinc burns with a 
bluish green flame, forming white zinc oxide (ZnO). Zinc 
does not tarnish in dry air, but ordinarily it becomes coated 
with a thin film of basic carbonate, which protects it some- 
what from further change. Commercial zinc interacts 
readily with acids and usually liberates hydrogen ; pure 
zinc acts very slowly. Like aluminium, it interacts with 
hot solutions of sodium and potassium hydroxides (514) ; it 
forms zincates and hydrogen, thus : — • 

2KOH + Zn = H2 + K2Zn02 

Potassium Hydroxide Zinc Hydrogen Potassium Zincate 

Zinc displaces most metals from their solutions (536). 
Ordinary zinc salts yield zinc ions (Zn++) in solutions. 

548. Uses of zinc. — Zinc is extensively used as an elec- 
trode in many kinds of batteries. Sheet zinc is used for 
roofs, gutters, pipes, parts of washing machines, and as a 
lining for tanks. The chief use of zinc is in making gal- 
vanized iron. This is iron covered with a thin layer of zinc 
and is made by dipping clean iron into melted zinc. 
The zinc protects the iron from air and moisture. Hence 
galvanized iron does not rust easily and is extensively used 
for netting, wire, roofs, pipes, cornices, and water tanks. 
Zinc shavings are used in the cyanide process of extracting 
gold (591). Zinc is an ingredient of many useful alloys, 
e.g. brass, bronze, and German silver (532). 

549. Zinc oxide and hydroxide. — Native zinc oxide 
is red, owing to the presence of manganese. The pure 
oxide (ZnO) is white when cold and yellow when hot. It 



MAGNESIUM - ZINC — MERCURY 445 

is fornicd when zinc burns, and is manufactured in this 
way or l)y heating zinc carbonate. It is often called zinc 
white or Chinese white, and large quantities are used in the 
manufacture of automobile tires and white rubber goods, 
and to make white paint. Paint made of zinc oxide is not 
discolored by sulphur compounds in the atmosphere (257, 
576). On account of its antiseptic j^roperties, zinc oxide 
is an ingredient of ointments. Zinc hydroxide (ZnCOHjo) 
is formed as a dull white precipitate by the interaction of 
sodium or potassium hydroxide and a solution of a zinc salt. 
An excess of the alkaUne hydroxide changes zinc hydroxide 
into a zincate (547, end). Zinc hydroxide, like aluminium 
hydroxide, has both acid and basic properties (519). Unlike 
aluminium hydroxide, however, it dissolves in ammonium 
hydroxide owing to the formation of a soluble complex com- 
pound (Zn(NH3)4(OH)2). 

550. Zinc sulphide, sulphate, and chloride. — Native 
zinc sulphide is yellow, brown, or black on account of im- 
purities. Pure zinc sulphide (ZnS) is white, and is formed 
as a jelly-like precipitate when hydrogen sulphide is passed 
into an alkahne or very weak acid solution of a zinc saU. 
A mixture of zinc sulphide and barium sulphate, called 
lithophone, is used as a white pigment in paints. Zinc 
sulphate (ZnS04) is formed by the interaction of zinc and 
dilute sulphuric acid. Large quantities are also made by 
roasting the sulphide in a hmited supply of oxygen and ex- 
tracting the sulphate with water. Thus prepared, it is a 
white, crystallized solid (ZnS04.7H20) which etSoresces in 
the air, and when heated to ioo° C. loses most of its water 
of crystallization. The crystallized salt is called white 
vitriol. It is used in dyeing and caUco printing, as a dis- 
infectant, and as a medicine. Like other zinc salts, it is 
poisonous. Zinc chloride (ZnCU) is a white, deUquescent 



446 PRACTICAL CHEMISTRY 

solid. It is used as a constituent of a mixture for filling 
teeth. Large quantities are used to preserve wood, es- 
pecially posts and railroad ties. Mixed with zinc oxide and 
water, it forms a cement. Cellulose (352) is slowly changed 
by zinc chloride into a plastic mass, which can be molded 
into different shapes, e.g. tubes, pails, sheets ; it is called 
fiber board. 

551. Tests for zinc. — The formation of the sulphide or hydroxide, 
as above described, serves as a test for zinc. A green incrustation is 
produced when zinc compounds are heated on charcoal and then 
moistened with cobaltous nitrate solution. (Compare 518, end.) 

552. Cadmium (Cd) occurs in zinc ores, and is extracted from the 
zinc dust condensed in the retorts (546). It is a white, lustrous, and 
rather soft metal. Cadmium is a constituent of certain fusible 
alloys (441). Wood's metal, for example, contains 12 per cent of 
cadmium. 

The most important compound is cadmium sulphide (CdS), which 
is a bright yellow soHd, formed by adding hydrogen sulphide to a 
solution of a cadmium compound. Its formation serves as the test 
for cadmium. It is used as an artist's color. 

553. Occurrence of mercury. — Native mercury is oc- 
casionally found in minute globules. The most abundant 
ore and the chief source of mercury is mercuric sulphide 
(cinnabar, HgS). The ore is extensively mined in Spain, 
Austria, and Italy ; in the United States large quantities 
are obtained in California and Texas. 

Mercury has been known for ages as quicksilver. The Latin name, 
hydrargyrum, which gives the symbol Hg, means " water silver." 

554. Metallurgy of mercury. — Mercury is readily pre- 
pared by roasting cinnabar in a current of air, and con- 
densing the vapor of the metal, thus: — 

HgS + O2 = Hg -f SO2 

Mercuric Sulphide Oxygen Mercury Sulphur Dioxide 



MAGNESIUM — ZINC — MERCURY 447 

The crude mercury is freed from soot by pressing it through linen 
or chamois leather. For accurate use it must be further purified by 
distiUing or by agitating with nitric acid (or feri-ic chloride) to remove 
the dissolved metals, such as lead or zinc. Mercury is sent into com- 
merce in strong iron flasks holding 75 pounds. 

555. Properties of mercury. — Mercury is a silvery metal, 
and is the only common one that is liquid at ordinary 
temperatures. It solidifies at about —39° C. and boils 
at about 357° C. It is a heavy metal, the specific gravity 
being about 13.6. Mercury is a good conductor of elec- 
tricity. 

Mercury does not tarnish in the air, unless sulphur com- 
pounds are present. At about 300° C. it combines slowly 
with oxygen to form red mercuric oxide (HgO). Hydro- 
chloric acid and cold sulphuric acid do not affect it; hot 
concentrated sulphuric acid oxidizes it, and nitric acid 
changes it into nitrates. It is displaced from solution by 
most metals (536). 

556. Amalgams are alloys of mercury. — Amalgamated zinc is 
used in certain electric batteries to prevent unnecessary loss of the 
zinc. Amalgams of some metals {e.g. tin, silver, gold) are used 
as a filling for teeth. Silver and gold form amalgams readily, 
and considerable mercury is used in extracting these precious metals 
from their ores (581, 591) . Care should be taken, while using mercury, 
not to let it come in contact with jewelry. 

557. Uses of mercury. — Mercury is used in ther- 
mometers, barometers, and some kinds of air pumps. Con- 
siderable is used in preparing certain medicines and ex- 
plosives {e.g. mercury fulminate, which is used in caps to 
explode gunpowder and nitroglycerin. It is also used in 
one method of making sodium hydroxide (456). 

The use of mercury in thermometers depends not only on the fact 
that it is a bright liquid between a wide range of temperature, but 
also on the uniform change of volume with change of temperature. 



448 



PRACTICAL CHEMISTRY 




The curve showing the relation of volume and temperature is almost 
a straight line (Fig. 204), that is, the expansion of mercury is regular. 

558. Two series 
of mercury com- 
pounds. — Mercury, 
like copper and iron, 
forms two classes of 
compounds — mer- 
curous and mercuric. 
The valence of mer- 
cury is I in mer- 
curous compounds 
and 2 in mercuric. 
Solutions of mercu- 
rous salts contain 
mercurous ions (Hg+), and of mercuric salts mercuric ions 
(Hg++). 

559. Mercurous and mercuric chlorides. — Mercurous 
chloride (HgCl) is a white, tasteless powder, insoluble in 
water. It is used as a medicine under the name of calomel. 
It is formed as a white precipitate when a chloride and mer- 
curous nitrate interact — a test for mercury in mercurous 
compounds. The equation is : — 

NaCl + HgNOs = HgCl + NaNOa ' 

Sodium Mercurous Mercurous Sodium 

Chloride Nitrate Chloride Nitrate 



200 3U0 

Temperature 

Fig. 204. — Curve showing regular change 
in volume of mercury with change of 
temperature 



This test is confirmed by adding ammonium hydroxide 
which blackens the precipitate. Mercuric chloride (HgCU) 
is a white, crystalline solid, soluble in water. It is prepared 
by heating a mixture of mercuric sulphate and sodium chlo- 
ride, thus : — 



MAGNESIUM — ZINC — MKRC I k^• 449 

HgSO., + 2NaCl = HgCl, + Na2S()4 

Mercuric Sodium Mercuric Sodium 

Sulphate Chloride Chloride Sulphate 

Mercuric chloride is a violent poison. The best antidote 
is the white of a raw egg. The albumin forms an insoluble 
mass with the poison, which may then be removed from the 
stomach. The common name of mercuric chloride is cor- 
rosive sublimate (or bichloride of mercury). It has power- 
ful antiseptic properties, and is extensively used in surgery 
to sterilize instruments and to protect wounds from the 
harmful action of germs ; taxidermists sometimes use it to 
preserve skins, and it has many serviceable applications 
as a medicine and disinfectant. It is usually used as a 
dilute solution (i part to 1000 parts of water). 

IMercuric chloride, when treated carefully with stannous 
chloride, is reduced first to white mercurous chloride 
and finally to a dark gray precipitate of finely divided 
mercury — the test for mercury in mercuric compounds. 
The equations for these reactions are : — 

2HgCl2 + SnCl2 = 2HgCl + SnCU 

Mercuric Stannous Mercurous Stannic 

Chloride Chloride Chloride Chloride 

2HgCl -f SnClo = 2Hg + SnCl4 

560. Other mercury compounds. — Native mercuric sul- 
phide or cinnabar (HgSj is a red, crystalline solid. When 
hydrogen sulphide is passed into a solution of a mercuric 
salt, mercuric sulphide is precipitated as a black powder ; 
this variety, when sublimed, changes into red crystals. 
Vermilion is artificial mercuric sulphide prepared by 
various processes. It has a brilliant red color and is used 
to make red paint. Mercurous nitrate (HgNO,-?) and 
mercuric nitrate (Hg(X03)2) ^re prepared by treating 



450 PRACTICAL CHEMISTRY 

mercury respectively with cold dilute nitric acid, and with 
hot concentrated nitric acid. They are white solids. 

EXERCISES 

1. State the properties and uses of magnesium. 

2. Starting with magnesium, how would you prepare in suc- 
cession MgO, magnesium hydroxide, MgCl2, magnesium carbonate, 
magnesium oxide? 

3. Write equations for (a) interaction of magnesium and sulphuric 
acid and (b) heating magnesium in nitrogen. 

4. Essay topics : (a) Asbestos, (b) Magnesia as a refractory 
material, (c) Stassfurt salts containing magnesium, (d) Dolomite. 
(e) Joseph Black's investigations of " magnesia alba." (/) Proper- 
ties of zinc and aluminium. 

5. Name the chief ores of zinc. Describe the metallurgy of zinc. 

6. Summarize the physical chemical properties of zinc. 

7. Starting with zinc how would you prepare in succession zinc ox- 
ide, ZnCla, zinc hydroxide, Na2Zn02, zinc sulphide, ZnClo, ZnCOs, 
zinc oxide, zinc? 

8. Topics for home study: (a) Zinc paints, (b) Galvanized iron. 

(c) Amalgams, (d) History of mercury, (e) Cinnabar. (/) Mer- 
curic oxide and oxygen, (g) Alloys of zinc. 

9. What are the tests for zinc? 

10. Describe the metallurgy and purification of mercury. 

11. Practical topics : (a) Suggest a proof of the volatility of mer- 
cury at ordinary temperatures, (b) What is the significance of 
" quick " in the word quicksilver? (c) Etymology of amalgam. 

(d) In what respect does mercury resemble bromine? (e) Name 
three metals which will float on mercury. (/) Why is mercury used in 
a barometer? 

12. Describe (a) mercurous chloride and (b) mercuric chloride. 
What is the commercial name of each? The use? 

13. State the tests for mercury. 

14. What is (a) magnesia, (b) Epsom salts, (c) galvanized iron, 
(d) Chinese white, {e) white vitriol, (/) calomel, (g) corrosive sublimate ? 

PROBLEMS 

1. Calculate the per cent of the metallic element in (a) magnesium 
oxide, zinc oxide, and mercuric oxide ; (b) Epsom salts, sphalerite? 
cinnabar, and smithsonite; (c) Mg2P207, H2Zn2Si05, Hg(N03)2. 



MAGNESIUM — ZINC — MERCURY 451 

2. Calculate the percentage composition of mercurous and mer- 
curic iodides, and show that these compounds illustrate the law of mul- 
tiple proportions. (Use exact atomic weights.) 

3. Write the ordinary and the ionic equations for (a) mercuric chlo- 
ride and hydrogen sulphide form mercuric sulphide and hydrochloric 
acid, (/') magnesium chloride and sodium hydroxide form magnesium hy- 
droxide and sodium chloride, (c) zinc hydroxide and sodium hydroxide 
form sodium zincate and water. 

4. Write the formulas of the following compounds by applying the 
principle of valence or by utilizing analogous formulas in this chapter : 
Magnesium bromide, magnesium nitrate, magnesium sulphide, zinc 
chromate, zinc carbonate, zinc acetate, zinc phosphate (ortho), mer- 
curous fluoride, mercuric sulphate, mercurous oxide. 

5. If the annual production of quicksilver in the United States 
were 20,600 flasks of 75 pounds each, and if this amount were made 
into corrosive sublimate, how many metric (2200 lb.) tons would be 
produced? 

6. What (a) weight of mercury, (b) weight of sulphur dioxide, 
(c) volume of sulphur dioxide (standard conditions) can be obtained 
from a metric ton of cinnabar (60 per cent pure) ? 

7. Calculate the atomic weights of magnesium, mercury, and zinc: 
(a) 16.0263 gm. of MgO give 47.8015 gm. of MgS04; {b) 16.03161 gm. 
of zinc give 19.9568 gm. of ZnO; (c) 118.3938 gm. of HgO give 109.6308 
gm. of mercury; (d) 177.1664 gm. of mercuric sulphide give 152.745 
gm. of mercury. (Use exact atomic weights.) 

8. What (a) weight and (b) volume (standard conditions) of oxygen 
will 79 gm. of mercuric oxide yield? 



CHAPTER XXXV 
TIN — LEAD 

561. Only one ore of tin. — Tin dioxide (cassiterite, 
tin stone, SnO-i) is the only available ore. It is not widely 
distributed. The ore was formerly mined in England 
(at Cornwall), but the chief . sources now are Australia, 
Tasmania, Bolivia, and the East Indian Islands, especially 
Banca and BilHton. None is mined in the United States. 

Tin is one of the oldest of metals. Many prehistoric bronzes con- 
tain tin. The Latin word stannum gives us the symbol Sn and the 
terms stannous and stannic. 

562. Metallurgy of tin. — The ore is roasted to remove 
sulphur and arsenic, and oxidize any iron present. The tin 
oxide is then reduced by heating it with coal in a reverber- 
atory furnace (Fig. 174). The equation is : — 

Sn02 + C = Sn + CO2 

Tin Dioxide Carbon Tin Carbon Dioxide 

The tin collects at the bottom of the furnace and is drawn off 
and cast into bars or masses, which are often called block tin. Usually 
it is purified by melting it slowly on an inclined hearth, so the low 
melting tin will flow away from the metallic impurities. This tin 
may be further purified by stirring the molten metal with a wooden 
pole, or by holding billets of wood beneath its surface. (Compare 
528, 6.) The impurities are oxidized by the escaping gases. Tin is also 
refined by electrolysis. 

563. Properties of tin. — Tin is a white, lustrous metal. 
It is soft and malleable, and can be readily cut and 

452 



TIN — LEAD 453 

hammered. It is softer than zinc, but harder than lead. 
Its specific gravity is 7.3. It melts at about 232° C, and 
when heated to a higher temperature it burns, forming 
white tin oxide (SnOo). 



Ordinary tin if kept below about 18° C. changes into gray tin, 
which is a dull looking powder. Sometimes objects containing tin, 
such as organ pipes, medals, and stat- 
ues, disintegrate owing to the forma- 
tion of powdery tin; once started, 
the " tin disease," as it is called, 
spreads rapidly (Fig. 205). 



'rtff^ >♦ -•- rf,-. .-'''• V-_ 









Concentrated hydrochloric acid 
changes it into stannous chloride 
(SnCl2) ; hot concentrated sul- 
phuric acid converts it into stan- 
nous sulphate (SnS04) ; and con- Fig. 205. — Sheet tin aflfected 
centrated nitric acid oxidizes it by " tin disease " (enlarged 
1 .^ Tj 1 J. one and one half times) 

to a white sohd known as meta- 

stannic acid or beta-stannic acid (usually designated by 
(H2Sn03)5). Certain metals precipitate tin from its solu- 
tions often as a grayish black, spongy mass filled with 
bright scales (536). 

564. Uses of tin. — Tin is so permanent in air, weak 
acids (like vinegar and fruit acids), and alkalies that it is 
extensively used as a protective coating for metals. Tin 
plate (also called sheet tin, or simply ''tin") is made by 
dipping very clean sheet iron into molten tin. Thus coated 
with a thin layer of tin, it is made into tinware, cans, and 
many useful objects. Copper coated with tin is made into 
vessels for cooking, and brass coated with tin is made into 
pins. Tinned iron or steel does not rust until the iron is 
exposed, and then the rusting proceeds rapidly. Tin pipes 
are used to convey Hquids,^.^. soda water, which act on lead. 



454 PRACTICAL CHEMISTRY 

Tin is also hammered into thin sheets called tin foil, though 
much tin foil contains lead. 

Tin is used in making useful alloys. Those containing a minor 
per cent of tin are bronze, gun metal, type metal, and fusible alloys 
(441, 532). Speculum metal contains about 30 per cent of tin. Al- 
loys containing considerable tin are Britannia metal (90 per cent), 
pewter (75 per cent), and solder (50 per cent). (Compare 532.) 

565. Two series of tin compounds. — Tin, like iron, copper, and 
mercury, forms two series of compounds — stannous and stannic. 
The valence of tin is 2 in stannous compounds and 4 in stannic. 
Stannous ions (Sn"^^) and stannic ions (Sn++++) are found in solu- 
tions of the respective salts. Stannous salts pass readily into the 
corresponding stannic salts. 

566. Stannous and stannic chlorides. — Stannous chlo- 
ride (SnCl-i) is formed by the interaction of hydrochloric 
acid and tin. From the concentrated solution a greenish 
salt crystallizes (SnCl2.2H20), known as tin crystals or 
tin salt. Stannous chloride hydrolyzes easily ; a strong 
solution deposits a basic salt (Sn(OH)Cl), i.e. a salt formed 
by substituting a non-metal for part of the hydroxyl groups 
of a base. To keep stannous chloride *' stannous," hydro- 
chloric acid and tin must be added to the solution. 
Stannous chloride can be quickly oxidized to stannic chlo- 
ride by mercuric chloride, thus : — 

SnCl2 + 2HgCl2 = SnCU + 2HgCl 

Stannous Mercuric Stannic Mercurous 
Chloride Chloride Chloride Chloride 

By an extension of the simplest idea of oxidation and reduction 
to include the negative element chlorine, stannous chloride may be 
said to be oxidized to stannic chloride and mercuric chloride to be 
reduced to mercurous chloride. (Compare 502, 559, end.) An excess 
of stannous chloride reduces the white mercurous chloride to gray or 
black metallic mercury; this serves as a test for tin (559, end). 



TIN — LEAD 455 

Stannic chloride (SnCU) is prepared by passing chlorine 
into stannous chloride solution, thus : — 

SnClo + Clo = SnCl4 

It is obtained industrially by passing dry chlorine over tin 
scrap (cuttings, cans, etc.). The stannic chloride, which 
boils at 114° C. is distilled from the other products. 

Stannous chloride is used as a reducing agent and as a mordant 
in dyeing and calico pnnting (522). Crystallized stannic chloride 
(SnCl4.5H20), known commercially as oxymuriate of tin, is also used 
as a mordant. Tin mordants produce brilliant colors. 

567. Other tin compounds. — Stannic chloride and 
bases form unstable stannic hydroxide, thus : — 

SnCl4 + 4NaOH = Sn(0H)4 + 4NaCl 

This hydroxide has acid properties. It is unstable, and 
by loss of water yields first alpha-stannic acid (HoSnOs) 
and finally stannic oxide (Sn02). The gelatinous precip- 
itate of stannic hydroxide dissolves in an excess of sodium 
hydroxide (519, 549), forming sodium stannate, thus: — 

Sn(0H)4 + 2NaOH = Na2Sn03 + 3H2O 

Stannic Sodium Sodium Water 

Hydroxide Hydroxide Stannate 

Sodium stannate is used in preparing fireproof cotton and in weight- 
ing silk. The cotton fabric is soaked in sodium stannate solution, 
washed, and dried, and then treated with ammonium sulphate solu- 
tion. The ammonium stannate thereby produced becomes stannic 
acid, which loses water and leaves stannic oxide as a non-inflammable 
precipitate. Silk fabrics, treated in a similar way, become heavier 
and more attractive in finish. The added tin compound is much 
greater (25 to 200 per cent) than the weight of the silk itself. Such 
silks are not durable. 



456 



PRACTICAL CHEMISTRY 



568. Only one ore of lead. — The most abundant native 
compound and the chief source of the metal is lead sulphide 
(galena, PbS). Other native compounds are the carbonate 
(cerussite, PbCOa) and the sulphate (anglesite, PbS04). 
Lead ore is found in the United States in the Middle West 
(Ilhnois, Iowa, Wisconsin, and Missouri), Colorado, Idaho, 
and Utah. 

Lead and its compounds have been used since the dawn of history. 
The Chinese have used it for ages to line chests in which tea is stored 




Fig. 206. — Desilverizing kettles in which lead is freed from silver 

and gold 

and transported. The Romans, who obtained it from Spain, called 
it plumbum nigrum, i.e. black lead, and used it for conveying water 
just as we do today. The symbol Pb comes from plumbum. 

569. Metallurgy of lead. — Lead is obtained from galena 
by first roasting the ore to change part of the sulphide to 
oxide. This product (sulphide and oxide) is then mixed 
with raw ore, iron oxide, hmestone, and coke, and smelted 
in a blast furnace. Complex changes take place, which 
consist essentially in (a) reduction of the lead oxide to lead 



TIN — LEAD 



457 



by the carbon and carbon monoxide, (b) transformation of 
lead sulphide to lead and iron sulphide, and (c) removal of 
silica and other impurities as a slag by the limestone. 

Lead produced by this process is impure and must be 
refined. The impurities make the lead hard and unfitted 
for most uses. The lead is first heated in a ''softening" 
furnace at a low temperature to oxidize the arsenic and 
antimony. The im- 
pure lead (containing 
chiefly gold and sil- 
ver) is m.elted with 
a small proportion 
of zinc in huge de- 
silverizing kettles 
(Fig. 206) ; the silver 
and gold together 
with the zinc and 
some lead form a 
crust on the top. 
This is skimmed off 
and heated in a re- 
tort to distill off the 
zinc ; the residue is 
next " cupelled," i.e. 




Fig. 207. — Casting refined lead into molds 

heated by a stream of air. By the 



latter process the lead is oxidized to Htharge (PbO) which 
is skimmed or blown off, leaving the silver and gold 
(581, second paragraph). These two metals are separated 
as described in 581 (last paragraph) and 592. 

The purified lead left in the desilverizing kettles is cast 
into molds by machinery (Fig. 207). 

Lead is also refined by electrolysis. The cathode is a sheet of pure 
lead, and the electrolytic solution is a mixture of lead fluosilicate 
(PbSiFe) mixed with gelatin. When the current passes, pure lead is 



458 PRACTICAL CHEMISTRY 

deposited on the cathode and the other metals remain attached to 
the remnant of the anode or sink to the bottom as mud. Sub- 
sequently the gold and silver as well as bismuth are recovered from 
the anode residues. (Compare 529.) 

570. Properties of lead. — Lead is a bluish metal. 
When scraped or cut, it has a brilliant luster, which soon 
disappears, owing to the formation of a film of oxide and 
basic carbonate. It is soft, and can be scratched with the 
finger nail ; it also discolors the hands, and when drawn 
across a rough surface it leaves a black mark. Lead is 
not tough nor very ductile and malleable, though it can be 
made into wire, rolled into sheets, and pressed while soft 
(just below the melting point) into pipe. It is a heavy 
metal, its specific gravity being 11.4; with the exception 
of mercury, it is the heaviest of the familiar metals. It 
melts at 327° C. 

571. Chemical conduct of lead. — Lead when heated 
strongly in air changes into oxides (mainly the monox- 
ide, PbO). Hydrochloric and sulphuric acids have httle 
effect upon compact lead. Nitric acid changes it into lead 
nitrate (Pb(N03)2). In the presence of air, weak acids 
like acetic acid (or vinegar), and acids from fruits and vege- 
tables change it into soluble, poisonous compounds ; hence 
cheap tin-plated vessels, which sometimes contain lead, 
should never be used in cooking. Soft water containing 
air, and especially carbon dioxide, dissolves lead ; and lead 
pipes should not be used to convey rain water or water con- 
taining ground gases. Certain metals, e.g. zinc and iron, 
precipitate lead from its solutions as a grayish mass, which 
often has a beautiful treehke appearance (536). 

572. Uses of lead. — Lead is extensively used as pipe. 
Lead pipe is not only used to convey water, but also as a 
sheath for electric cables, both overhead and underground. 



TIN — LEAD 459 

Sheet lead is used to cover roofs and to line sinks, cisterns, 
and the cells employed in some electrolytic processes. The 
lead chambers and some evaporating pans used in manu- 
facturing sulphuric acid are made of sheet lead. Shot and 
bullets are lead (alloyed with a little arsenic or antimony). 
Spongy lead is used in preparing the plates of storage bat- 
teries. Lead wool (very line wire) is used to calk pipe 
joints. 

Lead is used to make many useful alloys. Those con- 
taining considerable lead are type metal (lead, tin, 
antimony), solder (lead and tin), Britannia and Babbit 
metals, and pewter (532). Most fusible metals contain 
lead (441). 

573. Lead oxides. — There are three oxides. Lead mon- 
oxide (PbO) is a yellowish powder known cs massicot, or a 
buff-colored crystalline mass called litharge. It is formed 
by heating lead in a current of air. It is made this way, 
though considerable is obtained as a by-product in sepa- 
rating silver from lead (569). Large quantities are used in 
preparing some oils and varnishes, in making flint glass, 
and a glaze for pottery, and as the source of many lead com- 
pounds. Lead tetroxide (red lead or minium, Pb304) is a 
red powder, varying somewhat in color and composition. 
The pure compound is beheved to have the formula 
Pb2Pb04, i.e. plumbous plumbate. It is prepared by 
heating lead or lead monoxide at the right temperature 
(about 450° C, but not over 545° C). It is used in making 
flint glass. Pure grades are made into artists' paint, but 
the cheap variety is used to paint structural iron work 
(bridges, gasometers, etc.), hulls of vessels, and agricultural 
implements. A mixture of linseed oil and red lead is used 
by plumbers and gas fitters to make joints tight. Orange 
mineral has about the same composition as red lead, though 



46o PRACTICAL CHEMISTRY 

its color is lighter ; its uses are the same. Lead dioxide 
(Pb02) is a brown powder formed by treating lead tetroxide 
with nitric acid or by the action of bleaching powder on 
sodium plumbite (Na2Pb02, formed by dissolving lead 
hydroxide in sodium hydroxide). It is a strong oxidizing 
agent. It is extensively used as the essential ingredient of 
the positive plate of electric storage batteries. 

574. Lead carbonate (PbCOs) is found native as the 
transparent, crystallized mineral cerussite. It is obtained 
as a white powder by adding sodium bicarbonate solution 
to a solution of a lead salt. Sodium and potassium car- 
bonates, however, produce basic lead carbonates. The 
most important of these basic carbonates has the compo- 
sition corresponding to the formula 2PbC03.Pb(OH)2,and 
is known as white lead. 

575. Paints. — A paint consists essentially of a powder suspended 
in an oil, usually linseed oil, which " dries " (really oxidizes) to a 
tough film and sticks to a surface. The powder, which is often called 
a pigment, gives opacity and color to the paint. It also fills the 
minute holes in the dried oil film and thereby assists in protecting the 
surface of the painted object from the action of oxygen and moisture. 

576. White lead is a heavy, white powder which mixes 
well with linseed oil, and is used extensively as a white paint. 
It is also the basis of many colored paints, pigments being 
added to give the desired color. White lead paint has a 
marked covering power, i.e. it covers a surface well ; it 
also dries to a good finish. But it darkens on exposure to 
hydrogen sulphide (which is often present in the air of 
cities, 257), owing to the formation of black lead sulphide 
(PbS). In recent years other paint bodies, as the solids 
are called, have been mixed with, or substituted for, white 
lead, e.g. zinc oxide (549), kaolin, barium sulphate, and Htho- 
phone (a mixture of zinc sulphide and barium sulphate). 



TIN — LEAD 



461 




These are white soUds which do nol (hirkcn in the air, and 
they often improve the paint in other ways. 

577. Manufacture of white lead. — White lead is manu- 
factured by several processes. The Dutch process is the 
oldest, having been used as early as 1622. It is essentially 
the same today, though many details have been improved. 

Perforated disks of lead, called buckles, are put in earthenware pots, 
which have a separate compartment at the bottom, containing a weak 
solution of acetic acid (Fig. 208). 
These pots arc arranged in tiers in a 
large building, and spent tan bark is 
placed between each tier. The build- 
ing is now closed except openings for 
the entrance and exit of air and 
steam. The fermentation of the tan 
bark produces carbon dioxide and 
moisture ; heat is also liberated. The 
heat volatilizes the acetic acid which 
changes the lead into lead acetate. 
The moist carbon dioxide converts 
the lead acetate into basic lead car- 
bonate or white lead. The operation 
is allowed to proceed until the lead 
is entirely transformed — sixty to one hundred days. 

Commercial white lead is manufactured by other processes. In 
one, melted lead is blown (" atomized ") into a very fine powder by a 
jet of steam, and the powder is treated for several days with acetic 
acid, carbon dioxide, and air. 

578. Other lead compounds. — Native lead sulphide 

(PbS) is the mineral galena, the chief ore of lead. It re- 
sembles lead in appearance, but is harder and is usually 
crystallized as cubes, octahedrons, or their combinations 
(Fig. 200). It is obtained as a black precipitate by the 
interaction of hydrogen sulphide (or other soluble sul- 
phides) and a solution of a lead salt. Its formation is a 
test for lead (and of course for hydrogen sulphide). Lead 



Fig. 20S. — Earthenware ves- 
sel containing lead buckles 
to be made into white lead. 
Buckle before (lower) and 
after (upper) corrosion 



462 PRACTICAL CHEMISTRY 

chloride (PbCLi) is a white soUd formed by adding hydro- 
chloric acid or a soluble chloride to a cold solution of a lead 
salt. It dissolves in hot water. Lead sulphate (PbS04) 
is a white solid, formed by adding sulphuric acid or a soluble 
sulphate to a solution of a lead salt. It is very slightly 




Fig. 209. — Galena crystals (cube, octahedron and cube, octahedron) 

soluble in water, but soluble in concentrated sulphuric acid, 
hence crude sulphuric acid often contains lead sulphate. 
Lead chromate (PbCr04) is a yellow solid formed by adding 
a solution of a lead compound to a solution of potassium 
chromate or potassium dichromate. It is sometimes called 
chrome yellow and is used as a pigment. Its formation 
serves as a test for lead. 

EXERCISES 

1. Describe the metallurgy of (a) tin and (b) lead. 

2. Summarize the properties and uses of (a) tin and (b) lead. 

3. Name three alloys which contain large proportions of (a) tin and 

(b) lead. Name several alloys containing a minor proportion of 
(a) tin and {b) lead. 

4. Topics for home study: (a) History of tin. (b) Tin disease- 

(c) Tin plate industry, (d) Tin mordants, (e) Tin foil and its 
substitutes. (/) Different processes of making white Ifead. (g) Paints 
and painting. (//) History of lead, (i) Lead poisoning. 

5. State the tests for (a) tin and (b) lead. 

6. What are the properties and uses of each lead oxide? 

7. What tin compound is a reducing agent? 

8. Practical topics: (a) How would you test paint for lead? 
{b) What advantage has tin over lead for pipes? Lead over tin? 
(c) What is "tin"? Block tin? Tinfoil? Tinware? (d) What 
is red lead? White lead? Black lead? (e) How would you show 



TIN — LEAD 463 

the presence or absence of lead in a lead pencil? (/) Should lead 
paint be used on the walls of a chemical lai)orator3- ? Why? Zinc 
paint? Why? 

PROBLEMS 

1. Calculate the weight of (a) lead in 250 gm. of PbOi and (b) of tin 
in 250 gm. of SnOj. 

2. How many gm. of lead in (a) 200 gm. of galena, (b) in i kg. of 
litharge, (r) a metric ton (2200 lb.) of red lead? 

3. Write the formulas of the following compounds by applying the 
principle of valence : Lead fluoride, lead acetate, lead dichromate, 
stannous iodide, stannic bromide, stannous sulphide, stannic sulphide. 

4. Calculate the atomic weight of lead or tin from the following: 
(a) 16.2956 gm. of lead give 17.554 gm. of PbO ; (b) 4.9975 gm. of 
PbCl2 require 3.881 gm. of silver to precipitate the lead; (c) 25 gm. of 
tin give 31.8 gm. of stannic oxide (the specific heat of tin is 0.055); 
(d) 29.42 gm. of tin unite with 35.4 gm. of chlorine, and the vapor 
density of the compound is 8.303. 

5. Complete and balance the following : (a) SnClo + HgCl? 

= SnCU + ; (b) Sn + HNO3 = HzSnOg + 4NO2 H ; 

(c) SnCl2 + H2S = SnS -\ ; (d) Pb(X03)2 + HCl = PbCl2 H . 

6. Calculate the percentage composition of the two chlorides of tin 
and show how they illustrate the law of multiple proportions. 

7. A cube of lead is 6 cm. on each edge. How much does it weigh? 

8. A block of tin measures 30 X 10 X 5 cm. and weighs 10.95 kg. 
What is the specific gravity of the tin? 



CHAPTER XXXVI 

SILVER — PHOTOGRAPHY — GOLD 

579. Introduction. — Silver and gold are precious metals. 
They have been used for ages as ornaments and coins. 
The Latin names of these metals are argentum and aurum, 
from which the symbols Ag and Au are derived. 

580. Occurrence of silver. — Free silver occurs as flakes 
or wire in certain kinds of rock, though generally as alloys 
of gold and copper. The chief ore is silver sulphide (argen- 
tite, AgoS), which is usually associated with lead sulphide. 
Copper ores also contain silver. In fact, silver-bearing 
ores are an important source of silver. 

581. Metallurgy of silver. — Ores containing free silver, 
or silver compounds that can be easily changed into silver, 
are treated by the amalgamation process. The powdered 
ore is first changed, if necessary, into silver chloride by 
roasting with sodium chloride. The silver is freed by agi- 
tation with water and iron (or an iron compound) ; the 
simplest equation for this reaction is : — 

2AgCl + Fe = 2Ag + FeCl2 

Silver Chloride Iron Silver Ferrous Chloride 

The silver is extracted by adding mercury, which forms an 
amalgam with the silver (556). When the amalgam is 
heated, the mercury distils off and the silver — with some 
gold — remains behind. 

Silver is extracted from lead ores by the Parkes process. 
After the sulphur, arsenic, and other impurities have been 

464 



SILVER — PHOTOGRAPHY — GOLD 465 

removed from the lead ores by roasting, the Imal mixture 
of lead, silver, and gold is melted with about i per cent of 
zinc. As the mixture cools, an alloy of silver, gold, zinc, 
and a httle lead rises to the surface, solidifies, and is 
skimmed off. This process is repeated several times. 
The skimmings are heated in a retort to volatilize the zinc, 
and then in a shallow furnace (cupel furnace) to convert 
the lead into an oxide (PbO), which melts and runs off, 
leaving an alloy of silver and gold (569 and Fig. 206). 

Silver can be separated from the gold by several processes. 
In the older process the alloy is boiled with concentrated 
nitric (or sulphuric) acid ; the gold is not acted upon, but 
the silver forms a soluble silver salt (nitrate or sulphate). 
The silver is precipitated from the diluted solution by 
metaUic copper. Silver is also refined by electrolysis in 
much the same way as copper ; the anode is rich in silver 
and the solution is silver nitrate in nitric acid (529). 

582. Properties of silver. — Silver is a lustrous, white 
metal. It is harder than gold, but softer than copper. 
Like copper, it is ductile and malleable, and can be easily 
made into various shapes. Silver has a specific gravity of 
about 10.5, being heavier than copper, but lighter than lead. 
It melts at about 960° C. Silver conducts electricity the 
best of all metals, but it is too expensive for general use. 

583. Chemical conduct of silver. — Silver does not 
tarnish in air unless hydrogen sulphide is present, and then 
the famiUar brown (or black) film of silver sulphide (Ag2S) 
is produced. It also turns black when in contact with or- 
ganic sulphur compounds. For example, silver spoons be- 
come black in eggs or mustard. The tarnishing of house- 
hold silver is caused by hydrogen sulphide in illuminating 
gas or gas from burning coal. So-called '^ oxidized " 
silver is not oxidized, but coated with silver sulphide. 



466 PRACTICAL CHEMISTRY 

Certain metals, especially mercury, precipitate silver from 
solution in beautiful crystals (536). 

Silver is only very slightly acted upon by hydrochloric acid, 
and not at all by molten sodium hydroxide, potassium hy- 
droxide, or potassium nitrate. Nitric acid and hot concen- 
trated sulphuric acid change it into the nitrate (AgNOs) 
and the sulphate (Ag2S04) respectively. Sodium cyanide 
in the presence of air and water changes it into sodium sil- 
ver cyanide (NaAg(CN)2). 

Solutions of simple silver salts contain silver ions (Ag+), 
whereas complex salts yield complex ions, e.g. the silver- 
cyanogen ion (Ag(CN)2") and the silver-ammonium ion 

(Ag(NH3)2+). 

584. Cleaning silverware. — Tarnished silverware is 
usually cleaned by rubbing off the film of sulphide with a 
very soft abrasive. It can be safely and quickly cleaned 
by an electrolytic process. 

A piece of metallic aluminium and the tarnished object are im- 
mersed in a hot solution of sodium bicarbonate and sodium chloride, 
and kept in contact. As soon as the cleaning is accompHshed, the 
object is removed, thoroughly washed in clean, hot water, and dried. 
The proportions for household use are a teaspoonful each of baking 
soda and common salt to a quart of water. The best results are ob- 
tained when the solution is very hot and the two metals are in good 
contact. 

585. Uses of silver. — Silver is made into coins, jewelry, 
ornaments, and tableware. Pure silver is too soft for 
constant use, and is usually hardened by adding a small 
amount of copper. These alloys are used as coins and for 
jewelry. Silver coins of the United States and France 
contain 900 parts of silver to 100 of copper, and are called 
900 fine. British silver coins are 925 fine; this quahty is 
called sterling silver, and from it much ornamental and 



SILVER — PHOTOGRAPHY — GOLD 



467 



useful silverware is made. Large (juanlities of silver are 
used to plate other metals and to make silver e()m[)oun(ls, 
especially silver nitrate. 

586. Silver plating. — IMetals cheaper than silver, e.g. copper, can 
be readily coated or plated with pure silver. Plated silverware has 
the appearance of solid or pure silver. The object to be plated is 
carefully cleaned, and made the cathode in a solution of potassium 
(or sodium) silver cyanide; the anode is a plate of pure silver 
(Fig. 210). When the electric current is passed the silver dissolves 
from the anode and deposits 
on the cathode. The de- 
posit of silver is dull, but 
can be brightened by rub- 
bing. 

Mirrors and reflectors 
(especially for automobiles) 
are made by coating glass 
with silver. A mixture of silver nitrate and ammonium hydroxide is 
reduced to metallic silver, which sticks to the glass and is protected 
by varnishing it. 

587. Silver nitrate (AgNOs). — This is the most im- 
portant compound of silver. It is a white crystaUine solid, 
made from silver and nitric acid, thus : — 

3Ag + 4HNO3 = 3AgN03 + NO + 2H2O 




Fig. 210. — Silver platinj 



Silver 



Nitric Acid 



Silver 
Nitrate 



Nitric 
Oxide 



Water 



It is very soluble in water. It turns dark in contact with 
organic matter owing to reduction to metallic silver. For 
this reason it blackens the skin ; if applied long enough, it 
disintegrates the flesh, and is often used by surgeons to 
cauterize sores or abnormal growths. Silver nitrate is the 
essential substance used in making some indelible inks ; 
the cloth to which the ink is applied reduces the silver com- 
pound to black metallic silver. 



468 PRACTICAL CHEMISTRY 

588. Silver halides. — Silver chloride (AgCl) is made by adding 
hydrochloric acid or a chloride solution to a solution of a silver com- 
pound. It is a white, curdy solid, which soon turns violet in the light 
and finally black. It is converted by ammonium hydroxide into a 
soluble complex compound (Ag(NH3)2Cl), from which silver chloride 
can be reprecipitated by adding an excess of nitric acid. Silver bromide 
(AgBr) and silver iodide (Agl) are analogous to silver chloride in their 
properties and methods of formation ; they are used in photography. 

The formation and properties of silver chloride constitute the test 
for silver. 

589. Photography is based mainly on the fact that 
silver salts, especially the bromide and iodide, darken when 
exposed to the hght. 

The photograph is taken on a glass plate, or celluloid film coated 
on one side with a thin layer of gelatin containing very fine particles 
of silver bromide. The plate or film is exposed in the camera. The 
light that comes from the object being photographed passes through 
the lens and forms an image on the plate or film and changes the silver 
salt in proportion to the intensity of the light reflected from the ob- 
ject. The exposed plate, however, reveals no change until it is de- 
veloped. This process consists in immersing the plate in a solution 
of a reducing agent, e.g. hydroquinone, pyrogallic acid, or special 
mixtures. As the developer acts upon the silver salt on the plate, 
the image appears. This is really a deposit of finely divided silver 
which varies in thickness in proportion to the light that fell upon the 
plate, being thickest where the light was most intense. 

After the plate has been properly developed, it still contains some 
silver salt not altered by the light ; and if the salt were left on the 
plate or film, the image would be clouded and finally obliterated by 
the light. The image is, therefore, fixed by dissolving the silver salt 
with a solution of sodium thiosulphate (or " hyposulphite ") and 
washing the plate thoroughly. On the fixed plate the dark parts of 
the object appear light and the light parts dark ; and since the image 
is the reverse of the object, the plate in this condition is called a nega- 
tive (Fig. 211, left). 

The print, or photograph, is made on paper coated with a mixture 
much like the one on the plate, though less sensitive to light. The 
paper is laid upon the negative and exposed to the light, so the light 



SILVER — PHOTOGRAPHY — GOLD 



469 



must pass through the negative first. Since the negative obstructs the 
light in proportion to the thickness of the silver deposit, the dark and 
light parts are reversed and we thereby obtain a positive, i.e. a photo- 
graph which has approximately the same shading as the object 
(Fig. 211, right). 




Fig. 211. — Daguerre — a pioneer in photography (negative (left) and 
positive (right)) 
On some kinds of paper the image appears at once, but on others 
it must be developed and fixed. Subsequent treatment called toning 
produces special results. 

590. Occurrence of gold. — Gold is widely distributed, 
but not abundantly in many places. Its native compounds 
are few and rare ; the only important ones are the tellurides 
(compounds of tellurium, e.g. AuAgTe-z). It is never found 
pure, being alloyed with silver and occasionally with cop- 
per or iron. It is disseminated in fine, almost invisible, 
particles among ores of other metals, though not so abun- 
dantly as silver, and is recovered in the last stages of their 
purification (569, 581). Much gold is found in veins of 
quartz, and in the sand formed by the disintegration of 
gold-bearing rocks. 



470 



PRACTICAL CHEMISTRY 



nnonilnnnnnOnn 



591. Mining and metallurgy of gold. — Gold was for- 
merly mined by washing the gold-bearing sand in large pans 
or cradles. Now the sand is scooped up by huge dredgers 
and washed by machines. In placer mining and hydraulic 
mining, streams of water wash away the hghter materials, 
but leave the heavier gold behind. From this mixture, 

gold and silver are ex- 
tracted with mercury. 
In vein or quartz mining 
the lumps of gold-bearing 
quartz are crushed to a 
fine powder in stamp 
mills, i.e. in a row of 
huge iron mortars by 
hard pestles (Fig. 212). 
The moistened mass is 
passed over copper plates 
coated with mercury 
which collects or dis- 
solves the gold and other 
metals. The amalgam 
is heated, as in the metal- 
lurgy of silver, to remove 
the mercury, and the 
gold is extracted from 
the residue. 




Fig. 212. — Stamp mills for crushing 
gold ore to a fine powder. Cut away 
on the right to show stamps (2 and 
5 are lifted). Crushed ore passes 
through sieve (left) and the gold is 
caught by mercury on the plates 
(front). The rocky refuse is washed 
away. 



In the chlorination process the ore is treated with water containing 
chlorine or with bleaching powder and sulphuric acid ; this operation 
forms a soluble gold chloride (AuCl^), from which the gold is pre- 
cipitated as a fine powder by ferrous sulphate or other reducing 
agents. 

In the cyanide process the ore, usually low grade, or the 
slime from a previous extraction, is mixed with a weak 



SILVER — PHOTOGRAPHY — GOLD 47 1 

solution of sodium cyanide and exposed to the air ; this 
operation changes the gold into a soluble cyanide, thus : — 

4AU + 8NaCN + O2 + 2H0O = 4NaAu(CN)2 +4NaOH 

Gold Potassium Oxygen Water Sodium Gold Sodium 

Cyanide Cyanide Hydroxide 

The gold is separated from this solution by electrolysis 
or precipitated by zinc shavings (536). 

592. Refining gold. — Refining is accompHshed by part- 
ing or by electrolysis. By the old parting process known 
as quartation an alloy of gold and silver, in which the gold 
is about one fourth of the whole, is treated with nitric acid ; 
this operation changes the silver into the nitrate from which 
the pure gold may be readily removed. The metals can 
be parted by the method described under silver, viz. by 
boihng with concentrated nitric or sulphuric acid (581). 
By this treatment the silver is dissolved and the gold is 
left as a brownish, porous mass. 

These processes have been largely replaced by electro- 
lytic processes. In one, which is used in the United States 
mints, the solution is a mixture of gold chloride and hydro- 
chloric acid, the anode is an alloy rich in gold, and the 
cathode is pure gold. Gold is deposited on the cathode, 
and the silver forms silver chloride around the anode. 

The purity of gold is expressed in carats. Pure gold is 24 carats 
fine. An alloy, for example, containing 22 parts of gold and 2 parts 
of copper is 22 carat gold. 

593. Properties of gold. — Pure gold is a yellow metal ; 
the color of commercial gold varies with the alloying metal. 
It is nearly as soft as lead, and is the most ductile and 
malleable of all the metals. The leaf into which it can be 
beaten is very thin — in some cases requiring 1 10,000 leaves 
to make a thickness of i centimeter. Gold is one of the 



472 PRACTICAL CHEMISTRY 

heaviest metals, its specific gravity being about 19.3. It 
forms alloys with most metals. 

Air, oxygen, and most acids do not attack it, and for this 
reason it is sometimes called a noble metal. It is changed 
into gold chloride (AuCls) by chlorine and aqua regia (159, 
186). With sodium cyanide, as described in 591, it forms 
sodium gold cyanide (NaAu(CN)2). 

594. Uses of gold. — Pure gold is too soft for use as 
jewelry or coins, and it is usually alloyed with copper or 
silver. Gold coins contain gold and copper. The United 
States standard gold coins contain 90 per cent gold and 10 
per cent copper. Gold leaf of various grades is used to 
ornament books and signs. Jewelers use gold for many 
purposes; such gold varies from 12 to 22 carats in purity, 
though 14 or 18 carat gold is commonly used. Much 
jewelry is gold plated (595). On account of its mallea- 
biUty, feeble chemical action, and beauty, gold is used by 
dentists for Ming teeth. 

595. Gold compounds. — Gold like several other metals forms two 
series of compounds — aureus and auric, in which the gold has the 
valence of i and 3 respectively. Auric chloride (AuCls) is formed 
when gold is treated with chlorine or aqua regia. Auric chloride 
in dilute solution is reduced by stannous chloride solution to a beau- 
tiful purple precipitate; the latter is called "purple of Cassius," 
and is finely divided gold (a colloidal solution). Its formation is 
the test for gold. In gold plating, which is much the same as silver 
plating, the solution contains a potassium gold cyanide (KAu(CN)2 
orKAu(CN)4). 

EXERCISES 

1. Prepare a summary of the metallurgy of (a) silver and (b) gold. 

2. Describe in order the steps in taking a photograph. 

3. How is gold purified? What is 14 carat gold? 

4. Prepare a summary of the properties of (c) silver and (b) gold. 

5. If silver cost only ten cents a pound, for what would it probably 
be used? What is the present price of (a) silver and (b) gold? 



SILVER — PHOTOGRAPHY — GOLD 473 

6. Why is gold " valuable " ? What is stcrlinR silver? 

7. Review topics: (a) Aqua rcgia. (b) Amalgams, (c) Ions 
and ionization, {d) Valence, (e) Colloidal solutions. 

8. State uses of (a) silver and (b) gold that depend on the proper- 
ties. 

9. Write the formulas of these silver compounds by applying the 
principle of valence : Sulphide, hydroxide, o.xide, acetate, carbonate, 
nitrate, orthophosphate. 

10. As in Exercise 9 : Auric chloride, aureus bromide, auric sulphide, 
auric hydroxide, aurous chloride. 

11. Complete and balance : Ag2S04 + KBr = K2SO4 H . 

Write the final equation in ionic form. 

PROBLEMS 

1. Calculate the weight of (a) silver in i kg. of silver nitrate and 
(b) gold in I gm. of potassium auricyanide. 

2. Calculate the percentage composition of the two gold chlorides 
and show that they illustrate the law of multiple proportions. (Use 
e.xact atomic weights.) 

3. How many grams of gold in a 14 carat ring which weighs 14 gm.? 

4. (a) What weight of silver can be obtained from an American 
ten cent piece which weighs 2.44 gm.? (b) How much gold from an 
American gold coin weighing 3.75 gm.? 

5. How much silver chloride can be made from 47 gm. of silver 
nitrate ? 



CHAPTER XXXVII 

CHROMIUM — MANGANESE — PLATINUM — NICKEL 
AND COBALT — OTHER METALS 

596. Occurrence of chromium. — Metallic chromium is 
never found free. Its chief ore is ferrous chromite (chrome 
iron ore, Fe(Cr02)2). Traces of chromium occur in many 
minerals and rocks, e.g. emerald and serpentine, and verd 
antique marble. Chromite is mined in Greece, New Cal- 
edonia, New South Wales, and Turkey. 

597. Preparation, properties, and uses of chromium. — Chromiiim 
is produced by reducing chromium trioxide (CrsOs) with granulated 
aluminium (517). 

Chromium is a silvery, crystalHne, hard, brittle metal. Its specific 
gravity is about 6.9 and its melting point is about 1520° C. It is not 
oxidized by air at ordinary temperatures. 

Chromium is used to harden the steel made into armor plate, pro- 
jectiles, safes, vaults, and parts of the stamp mills used to crush 
gold-bearing quartz (591). This hardened steel is called chrome 
steel (499). It forms other hard alloys. One commercial form of 
chromium is an alloy of 65 to 80 per cent chromium, a httle carbon, 
and the rest iron; this alloy is called ferrochrome. Another alloy, 
called nichrome or chromel, contains nickel. 

598. Chromates and dichromates. — Chromates are 
salts of chromic acid (H2Cr04) which is formed when the 
red chromium oxide (chromic anhydride, CrOs) is dis- 
solved in water. Potassium chromate (K2Cr04) is the 
commonest chromate ; it is a lemon-yellow, crystalline 
solid, very soluble in water. Acids change it into the di- 
chromate, thus : — 

474 



CHROMIUM 475 

2K2Cr04 + HoSOi = K2Cr207 -f KoSO, + H,0 

Potassium Sulphuric Potassium Potassium Water 
Chromate Acid Dichromate Sulphate- 

Lead chromate (PbCrOi) is a yellow solid, formed by adding 
a lead salt solution to potassium chromate (or dichromate). 
Its formation is a test for chromium (and lead, 578). It 
is known as chrome yellow, and is used in making yellow 
paint. Potassium dichromate (sometimes called bi- 
chromate) (KoCroO?) is a red solid. It forms large an- 
hydrous crystals. It is less soluble in water than potassium 
chromate, and its solution contains both chromate (Cr0.r~) 
and dichromate (Cr207~~) ions. AlkaHes change it into a 
chromate, thus : — 

K2Cro07 + 2KOH = 2K2Cr04 + H2O 

Potassium Potassium Potassium Water 

Dichromate Hydroxide Chromate 

Potassium dichromate is used in dyeing, calico printing, and tan- 
ning, in bleaching oils, and in manufacturing other chromium com- 
pounds and dyestufls. 

Potassium dichromate is an oxidizing agent. When hydrochloric 
acid is added to potassium dichromate, the oxygen of the dichromate 
oxidizes the hydrogen of the acid and liberates chlorine, thus : — 

KsCr.O; + 14HCI = 2KCI + 2CrCl3 -f 3CI2 + 7H2O 

Potassium Hydrochloric Potassium Chromic Chlorine Water 

Dichromate Acid Chloride Chloride 

The equation for the reaction in the case of ferrous sulphate is : — 
KzCraO; + 7H2SO4 + 6FeS04 = 3Fe2(S04)3 + Cr2(S04)3 + K2SO4 -f- 7H-.0 

Ferrous Ferric Chromic 

Sulphate Sulphate Sulphate 

Sodium dichromate (NaoCroO;) is a red solid much like potassium 
dichromate, which it has largely displaced. 

Potassium chromate is manufactured by roasting chrome iron ore 
with lime and potassium carbonate. The potassium chromate ex- 
tracted from the mass is changed by sulphuric acid into potassium di- 
chromate. 



476 PRACTICAL CHEMISTRY 

Potassium chromatc is also formed as a yellow mass by fusing on 
porcelain or platinum a mixture of a chromium compound, potassium 
carbonate, and potassium nitrate — a test for chromium. 

599. Chrome alum (K2Cr2 (804)4. 24H2O) is a purple, 
crystalline solid (521). 

Chrome alum is used as a mordant in dyeing and calico printing 
(522). It is also used in tanning leather because it readily forms 
chromium hydroxide (Cr(0H)3) which changes the hide into a rela- 
tively insoluble compound. 

600. Other chromium compounds. — Chromic oxide (Cr203) is a 
bright green powder prepared by heating chromic hydroxide 
(Cr(0H)3). It is the basis of the chrome green pigments used to 
color glass and porcelain. When chromium compounds are heated 
with borax they color the bead green, owing to this oxide (458). 

There are several chromic hydroxides. The typical one is a bluish 
solid formed by the interaction of a chromic compound {e.g. chrome 
alum) and an alkaline hydroxide, carbonate, or sulphide. The chromic 
hydroxide is soluble in an excess of sodiam (or potassium) hydroxide. 
That is, it is changed into a soluble chromite, just as aluminium hy- 
droxide forms soluble aluminates. Unlike aluminates, however, the 
chromites are changed back into chromic hydroxide by boiling. 

When concentrated sulphuric acid is added to a saturated solution 
of potassium dichromate (or chromate), chromium trioxide (CrOa) 
separates as long, bright red crystals ; this oxide is often called chromic 
acid (598). It is a vigorous oxidizing agent. 

601. Occurrence of manganese. — This metal is not 
found free in nature, but its oxides and hydroxides are 
widely distributed and rather abundant. The chief com- 
pound is manganese dioxide (pyrolusite, Mn02). 

602. Preparation, properties, and uses of manganese. — Manga- 
nese is prepared by heating manganese dioxide with charcoal in an 
electric furnace, or by reducing the oxide with aluminium (517). The 
metal is grayish, hard, and brittle. It melts at 1 225° C. Manganese, 
alloyed with iron, is used in making steel (499). Spiegel iron con- 
tains from 5 to 20 per cent of manganese, while ferromanganese con- 
tains 20 per cent or more. 



MANGANESE 477 

603. Manganese dioxide (MnOo) is 11 black solid and is 
often called black oxide of manganese. It is an oxidizing 
agent. When heated it yields oxygen. When heated with 
hydrochloric acid (144) manganous chloride, chlorine, and 
water result, thus : — 

MnOs + 4HCI = MnCl. + Clo + 2H,0 

Manganese Hydrochloric Manganese Chlorine Water 
Dioxide Acid Chloride 

It colors glass and borax a beautiful amethyst, and is often 
used in glass making to neutralize the green color caused 
by impurities. Large quantities are used in the manu- 
facture of glass, dry batteries, and manganese alloys. 

604. Potassium permanganate (KMn04) is a dark purple, 
glistening, crystalline solid. It is very soluble in water, 
and the solution is red, purple, or black, according to the 
concentration. The solution contains permanganate ions 
(Mn04~). Potassium permanganate is used as an oxidiz- 
ing agent, a disinfectant, and an antiseptic. 

The uses of potassium permanganate depend mainly upon its 
oxidizing power. With sulphuric acid the action is thus : — 

2KMn04 -h 3H2SO4 - 5O H- 2:\InS04 -h K2SO4 + 3H0O 

Potassium Sulphuric Oxj-gen Manganese Potassium Water 

Permanganate Acid Sulphate Sulphate 

The liberated oxygen oxidizes any organic matter present, and the 
solution becomes colorless (or brownish) owing to the reduction of 
the potassium permanganate to colorless manganese compounds. 

605. Other manganese compounds. — The chloride (MnCl^) and 
sulphate (MnS04) are pink, crystalline salts. The sulphide (MnS) 
is a flesh-colored precipitate formed by adding ammonium sulphide 
to the solution of a manganese salt, the color distinguishing it from 
all other sulphides ; its formation serves as a test for manganese. 
Another test is the formation of green potassium manganate 
(KoMn04) by fusing a mixture of a manganese compound, potassium 
hydroxide (or carbonate), and potassium nitrate. Sodium manganate 
(Xa2Mn04) is used in solution as a disinfectant. 



478 PRACTICAL CHEMISTRY 

606. Occurrence of platinum. — Platinum occurs as the 
chief ingredient of an alloy called platinumore. The asso- 
ciated metals are osmium, iridium, and palladium; iron, 
gold, and copper are usually present. Only one native com- 
pound is known, viz. platinum arsenide (sperrylite, PtAs2). 

607. Preparation of platinum. — Platinum is obtained by boiling 
the ore with aqua rcgia, then precipitating with ammonium chloride, 
and heating. This spongy platinum is melted, and hammered while 
hot into a compact form. It is a scarce and expensive metal. 

608. Properties and uses of platinum. — Platinum is a 
lustrous, gray-white, somewhat soft metal. It is malleable 
and ductile. Sheet platinum is cut into squares — the 
famihar platinum foil of the laboratory, or made into cruci- 
bles, dishes, and stills. Its use in these forms is based 
partly on its high melting point (1755°) and partly on its 
resistance to acids and other corrosive chemicals. Although 
it is attacked by fused caustic alkaHes {e.g. NaOH), low 
melting metals {e.g. lead), and aqua regia, platinum is prac- 
tically indispensable in the chemical laboratory and is used 
in many chemical processes involving accurate analysis. 

Platinum is a good conductor of electricity and is made 
into small electrodes. Formerly large quantities were con- 
sumed in electrical apparatus, especially as the " sealed in " 
wires in electric Hght bulbs, but this need is now met by an 
alloy of iron and nickel called platinite (499, 610). 

Platinum is a very heavy metal. Its specific gravity is 
about 21. (Lead is 11. 4.) 

In the form of a black, porous mass it is called spongy 
platinum, and a still finer form is called platinum black. 
Asbestos coated with platinum is used as the catalyzer in 
the contact method for making sulphuric acid (269, 270). 

Platinum forms low melting alloys with other metals, and should 
never be heated \nth. lead, similar metals, or their compounds. With 



NICKEL 479 

iridium, however, it forms a very hard alloy of which certain standard 
metric apparatus is made. Platinum is used in making rings and as 
mountings for gems. 

609. Occurrence and properties of nickel. — Small 
amounts of metallic nickel are found in meteorites. The 
chief ores are nickel-bearino; iron sulphides, which are abun- 
dant in the Sudbury district, Canada, and the sihcates 
found in New Caledonia. 

Nickel is a silver-white metal, which takes a brilliant 
poHsh. It is ductile, hard, malleable, tenacious, and does 
not tarnish in the air. It is attracted by a magnet. 

610. Uses of nickel. — Nickel is an important ingredient 
of coins and alloys. 

The per cent of nickel is 12 in the United States cent and 25 in the 
five-cent piece. German silver contains from 15 to 25 per cent of 
nickel (532). Platinite is an alloy of nickel (46 per cent) and iron; 
it is used as a substitute for platinum (499, 608). Monel metal con- 
tains nickel (70 per cent) and copper (28 per cent) ; it is stronger 
than ordinary steel, is not attacked by acids, and can be cast and 
machined. 

Nickel is used to coat or plate other metals, especially 
iron and brass. Nickel plating is done by electrolysis, as 
in silver and gold plating, though the electrolytic solution 
contains ammonium nickel sulphate ( (NH4)2Ni(S04)2), not 
a cyanide (586, 594, 595). The deposit of nickel is hard, 
brilliant, and durable. An important use of nickel is in 
the manufacture of nickel steel (5 per cent nickel) which 
is used for the armor plate and turrets of battleships (499). 

611. Nickel compounds. — Nickel forms two series of compounds 
— the nickelous and the nickelic. The nickelous are more common 
and many of them are green. The test for nickel is the formation 
of apple-green nickelous hydroxide (Ni(OH)o) by the interaction of 
an alkali and a dissolved nickel salt. 



48o PRACTICAL CHEMISTRY 

612. Cobalt (Co) generally occurs combined with arsenic and sul- 
phur in complex minerals, and is often associated with nickel com- 
pounds. It is a lustrous metal with a reddish tinge. It is harder than 
iron but less magnetic. 

Cobalt forms two series of compounds — the cobaltous and the 
cobaltic. The cobaltous compounds are more common. Cobaltous 
nitrate (CoCNOs)^) is a red soHd, which crystallizes with six molecules 
of water of crystallization. The hydrated compound loses water 
readily and turns blue when heated. 

Some cobalt compounds are used to color glass, porcelain, and 
paper, especially a complex compound known as smalt or smalt blue. 
The blue color produced by fusing cobalt compounds into a borax 
bead is a test for cobalt. Another test is the precipitation of yellow 
potassium cobaltinitrite (K3Co(N03)6) by the addition of potassium 
chloride, potassium nitrite, and acetic acid to a solution of a cobaltous 
compound. 

613. Molybdenum (Mo), tungsten (W), and uranium (U) are 
metallic elements related to chromium. Ammonium molybdate 
( (NH4)2Mo04) is used to detect and determine phosphorus in ferti- 
lizers (426). Tungsten and molybdenum are used to make special 
steels (499) ; and tungsten is the filament of electric light bulbs ; 
sodium tungstate is used for making cloth fireproof. Uranium com- 
pounds are obtained chiefly from pitchblende and uraninite. Salts 
of uranium (e.g. sodium uranate, Na2U207.6H20) are used in making 
fluorescent glass ; such glass is green by transmitted light and yellow 
by reflected light. Uranium is a radioactive element (618). 

614. Cerium (Ce) and thorium (Th) are members of the tin-lead 
family. They are constituents of rare minerals. Their compounds 
are prepared from monazite sand. A mixture of the oxides of thorium 
and cerium composes the Welsbach mantle (338) . In making mantles, 
a cotton bag is dipped into a solution of thorium and cerium nitrates 
and burned. The cotton is consumed and the nitrates are changed 
into a firm mass of oxides. Thorium is a radioactive element (618). 

EXERCISES 

1. Describe the preparation of (a) chromium and (b) manganese by 
the aluminothermic method. 

2. State test for (a) chromium and (b) manganese. 



PROBLEMS 481 

3. Review topics: (a) Uses of manganese dioxide, (h) Oxidation 
with potassium permanganate. (< ) Sj)ecial steels, {d) Alums. 
((•) Lead chromate. 

4. Starting with Mn()2 how would you prepare in succession MnCU 
and manganese sulphide ? Starting with Fe(;Cr()2)2 how would you pre- 
pare K2Cr04, K2Cr207, potassium chromate, lead chromate? 

5. Write the formulas of the chromate, dichromate, manganatc, 
and permanganate corresponding to NH4, calcium, Pb", Al, mag- 
nesium, Ag, Na. 

6. What is ferrochrome, black oxide of manganese, chrome 3'ellow, 
chrome alum, pyrolusite, spiegel iron? 

7. Enumerate the uses of platinum based on its properties. 

8. Apply Exercise 7 to (a) nickel, (b) tungsten, (c) cerium and 
thorium. 

PROBLEMS 

1. What weight of the pure metals can be prepared by the inter- 
action of aluminium and (a) 2 kg. of manganese dioxide, and (b) 2000 gm. 
of chromium trioxide? 

2. How much potassium chromate can be made from potassium hy- 
droxide and 299 gm. of the other compound? 

3. What weight of potassium dichromate can be made from 3 tons 
of potassium chromate? 

4. Complete and balance the following : (a) CaCr04 + K2SO4 = 

+ K2Cr04; (6) Pb(N03)2 + = PbCr04 + KNO3; (c) Mn02 + 

K2CO3 + O = K2Mn04 + . 

5. What is the atomic weight of chromium, if 6.6595 gm. of am- 
monium dichromate yield 4.0187 gm. of chromic oxide? (Use exact 
atomic weights.) 

6. A piece of platinum foil measuring 10.5 cm. by 1.5 cm. weighs 
0.723 gm. Into how many pieces, weighing i dg., may it be divided? 

7. The specific heat of platinum is 0.0324. According to analysis, 
35.5 gm. of chlorine unite with 48.6 gm. of platinum to form platinic 
chloride. What is (a) the atomic weight of platinum and (b) the formula 
of platinic chloride ? 



CIL\PTER XXXVIII 
RADIUM AND RADIOACTIVITY 

615. What is radium ? — Radium is a metallic element 
which belongs to the calcium family (^399 ^ . It is a constit- 
uent of the rare minerals camotite and pitchblende. Car- 
notite is mined chiefly in Colorado and Utah, and pitch- 
blende in Czechoslovakia. The proportion of radium in 
these minerals is minute, only a few milligrams to the ten. 
But this small proportion of radium, together with barium, 
is carefully extracted by a laborious chemical process ; the 
radium is then separated from the other metals as radium 
chloride or bromide by fractional cn'stallization. 

Radium itseH is never extracted. The term radium as 
usually used means a compound, e.g. the commercial salt is 
radium bromide (RaBr^). Since the supply of radium ore 
is exceedingly limited and the extraction is expensive, the 
price of radium compounds is high, about $100,000 a gram 
(of actual radium in the salt*. 

616. Discovery of radium. — About iSc)6 Henri Becquerel dis- 
covered that uranium compounds affect a photographic plate wrapped 
in black paper just as light does. Some minerals containing uraniimi 
compounds, particularly pitchblende, were later (1898) found by 
Madame Curie (Fig. 213) to be more active than uranium compounds. 
She studied pitchblende carefully, and subsequently in collaboration 
with her husband extracted from this mineral a minute quantity- of a 
new substance which was exceedingly active. Madame Curie gave 
the name radium to the elementar\- constituent in it. Since then, 
although ver>' small amoimts of radium compoimds are available, 
radium and its compounds have been zealously studied by ^ladame 
Curie and others. 

482 



IL\DirM AXD RADIOACTRTTi' 



4S3 




617. General properties of radium and radium com- 
pounds. — The general properties of radium show that it 
belongs to the alkaline earth family {i.e. calcium, strontium, 
and barium L Metallic radium was isolated by Madame 
Curie in 1910. It is much like barium. Both are silvery 
metals which tarnish in the air and decompose water at 
ordinary' temperatures. 

Radium forms salts like those of calcium and barium, 
e.g. a soluble chloride (RaClsX and an insoluble sulphate 
(RaS04) and carbonate CRaCOsV Radium compounds Hke 
those of calcium and strontium color the Bunsen flame red. 

618. What is radioactivity ? — Besides the properties 
just enumerated, radium compounds have special properties 
which are conspicuously different from those of most sub- 
stances. Let us consider three of these properties, 
(i) Radium compounds spontuneously ezoke considerable 
heat. It has been calculated that one gram of a pure 
radium salt gives off over 100 calories per hour. i.e. liberates 



484 



PRACTICAL CHEMISTRY 



wm 



tlMttmf. 



enough heat every hour to raise 
a Uttle more than its own weight 
of water from the freezing point 
to the boiling point. (2) Radium 
compounds affect a photographic 
plate just as light does. If a 
tube containing a radium com- 
pound is left a short time on a 



Fig. 214. — Effect of radium 
compounds upon a photo- 
graphic plate. (This was photographic plate wrapped in 

produced by slowly mov- ^^^^^ ^^ ^^^^ ^^^^^ gj^^jy 

ing a small tube containing . . • i i 

radium bromide across the ^cross it, an image IS produced 
plate (wrapped in black when the plate is developed 

paper), and then develop- (pjg 214). Radium compounds 

mg e p a e. actually photograph themselves 

(Fig. 215). (3) Radium compou7ids ionize the surrounding 
air, i.e. make it a conductor of electricity. Thus, radium 
compounds discharge an electroscope. An electroscope 
(Fig. 216) contains tv/o thin strips of metal {e.g. gold 
or aluminium), which 
separate when the elec- 
troscope is charged wdth 
electricity. Radium 
compounds, if brought 
near a charged electro- 
scope, ionize the air, 
which permits the es- 
cape of electricity from 
the electroscope ; hence 
the leaves fall together. 
The electroscope is used 
to detect radium com- 

- . Fig. 215. — Dish of radium bromide 

pounds, and very sen- photographed by itself in a dark 
sitive instruments are room 




RADIUM AND RADIOACTIVITY 



48: 




essential in determining the proportion of radium in mix- 
tures. 

The special properties exhibited by radium compounds 
are called radioactive properties ; the term radioactivity is 
often used to include these properties. 
Similar properties, though less in de- 
gree, are possessed by compounds of 
other elements, e.g. uranium and 
thorium. 

619. Interpretation of radioactivity. 
It was first thought that the special ^'^- ''^; ~ ^^^^^^ 

of an electroscope 

properties of radium compounds were 
due to rays or radiations ; hence the name radium. 
Many interesting experiments show that radioactivity is 
caused by the spontaneous emission of two kinds of elec- 
trically charged particles, called alpha (a) and beta (/3). 
The emission of beta particles is accompanied by pulsations 
in the ether called gamma (7) rays. 

The alpha particles are positively charged and move 
with great velocity — in some cases as great 
as 14,000 miles a second ; the muzzle velocity 
of a bullet is about i of a mile a second. 
Each alpha particle carries two unit charges of 
positive electricity. To the alpha particles are 
due many of the electrical phenomena of ra- 
dioactive substances, such as ionizing the air. 
^s "^ th ~ Although alpha particles move very fast in 
scope straight lines, they do not travel very far ; they 

are completely stopped by the time they have 
plowed through the air to a depth of 3 to 8 centimeters. 
They are almost entirely stopped by a thin sheet of 
paper and by aluminium leaf o.i mm. thick. Alpha 
particles are identical with positively charged helium 




486 PRACTICAL CHEMISTRY 

atoms (127, 620, 621) ; their weight is four times that of a 
hydrogen atom. 

A simple instrument called the spinthariscope (Fig. 217) shows in a 
striking way that particles are being shot off continuously from a 
radium compound. The screen S is coated with zinc sulphide and 
on the needle R there is a minute quantity of radium bromide. Upon 
looking into the spinthariscope through the lens, minute flashes of 
light are seen on the screen. The flashes are due to the impacts of the 
steady stream of alpha particles which bombard the screen and pro- 
duce fluorescence in the zinc sulphide. 

The beta particles are electrons, i.e. particles of negative 
electricity, moving with varying velocity, which sometimes 
reaches two- thirds the velocity of hght (186,000 miles a 
second). The beta particles are very light, their weight 
being about tf46 oi the weight of a hydrogen atom. The 
beta particles produce most of the photographic effects. 
They are stopped by aluminium i cm. thick. 

The gamma rays have the least ionizing and photographic 
power, but they are the most penetrating. They pass 
readily through thick layers of metal. Glass tubes con- 
taining radium salts are enclosed in thick lead vessels to 
absorb the gamma rays. Gamma rays are not material 
particles, but ether waves of the same nature as X-rays. 

The heat evolved by radioactive substances is due to 
the fact that the rapidly moving alpha and beta particles 
are stopped by the air, metals, and the radioactive sohd 
itself. 

620. Radium is decomposing spontaneously. — Al- 
though radium is an element which possesses many prop- 
erties hke those of the other eighty or more elements, it 
differs from most of them in being unstable. That is, 
many observations show that radium is slowly disinte- 
grating. Thus, we have already stated that the alpha 



RADIUM AND RADIOACTIVITY 487 

particles arc charged helium atoms. Indeed, it has been 
shown many times, that when alpha particles (collected in a 
tube) lose their charge of electricity, the spectrum of helium 
appears. Besides, the rate at which heUum is given off 
by radium has been measured. Another gas has been ob- 
tained from radium, viz. radium emanation or, as it is more 
often called, niton. It is given off continuously by radium 
compounds. Moreover, it belongs to the same family as 
helium and argon (i.e. the zero group in the periodic classi- 
fication, 399), and has properties much Uke those of argon. 

The two elementary gases, helium and niton, are pro- 
duced spontaneously. That is, they are coming off con- 
tinuously from all radium compounds independently of tem- 
perature and other conditions. We conclude that the radium 
atom itself is disintegrating spontaneously. This means 
that the atom of one element (radium) is transforming 
itself into the atoms of two other elements (helium and 
niton). Unlike other chemical transformations, however, 
it cannot be hastened or retarded. It goes on unceasingly 
and unvaryingly at temperatures between liquid air and 
the electric furnace. Furthermore, this transformation 
means that radium is slowly disappearing. The change is 
not rapid. Experiments which we cannot discuss here 
show that half a given weight of radium will disappear in 
about 2000 years, half of the residue in another 2000 years, 
and so on. Niton is also disintegrating. Its rate, however, 
is rapid ; the half period, as it is called, is 5.5 days. 

621. The radium disintegration series. — Helium and 
niton are not the only elements formed by the disintegration 
of radium. Indeed, radium itself is a product of uranium. 
Hence uranium, the heaviest of all the elements, is regarded 
as the parent substance in the disintegration series. The 
others in the series are uranium Xi, uranium Xo, uranium 2, 



488 PRACTICAL CHEMISTRY 

ionium, radium, niton, radium A, B, C, Ci, D, E, F, and G. 

All of these products are believed to be chemical elements ; 
some are very unstable, the half period being only a few 
minutes. Helium is not a member of the series, but is 
given off in some of the transitions. Electrons are also 
expelled in some cases. Evidence indicates that the final 
product of disintegration is radio-lead. 

622. Atomic weights and the disintegration series. — 
The disintegration of certain elements in this series is ac- 
companied by the expulsion of an alpha particle, an electron, 
or both. An electron has a neghgible weight, but a hehum 
atom, which is an alpha particle minus the electric charges, 
has the weight 4. Hence the loss of a helium atom lowers 
an atomic weight by 4 units. Let us take two examples, 
(i) In passing from a uranium atom to a radium atom, 
three helium atoms are lost; and from radium to niton, 
one is lost. Therefore, the atomic weight of radium should 
be 12 units (3 X 4) less than uranium, and of niton 4 less 
than radium. By the table (back inside cover) we see that 
uranium has the atomic weight 238.2, radium 226, and 
niton 222.4. (2) Eight helium atoms are lost in passing 
from uranium to radium G (the final product). Hence 
the final product should have the atomic weight 206 
{i.e. 238 — 8 X 4). The atomic weight of the lead isolated 
from uranium ores was found to be 206.4 by exceptionally 
accurate experiments by Richards (Fig. 82). 

The atomic weight of lead from other {i.e. non-radioactive) sources 
is 207.2, which is actually — not estimated — higher than that of 
so-called radio-lead. The two forms of lead have identical chemical 
properties, e.g. form compounds exactly alike in exactly the same way. 
They differ only in atomic weight. Elements which differ in atomic 
weight but not in properties are called isotopes or isotopic elements. 
Other elements besides lead are isotopic. 



RADIUM AND RADIOACTIVITY 489 

623. Uses of radium. -The products from radium, es- 
pecially beta particles and gamma rays, have a powerful 
effect on living matter, and are utilized to cure certain 
skin diseases. Much study is being made in this field. 
The radium compound itself is so expensive, it is seldom 
used directly. Since radium compounds are constantly 
giving off radium emanation (620) which disintegrates and 
produces beta particles and gamma rays, the emanation 
is used. It is collected in tiny glass tubes which can be 
placed upon or within the flesh. 

A luminous mixture containing zinc sulphide and a mi- 
nute quantity of a radium compound is used on watch dials, 
push buttons, door numbers, and electric light chains. 
The cost of the radium is only a few cents for each object. 
The action is the same as in the spinthariscope (Fig. 217). 

624. Other radioactive elements. — Besides uranium and 
radium, the element thorium is radioactive, though to a 
much less degree than radium. Thorium disintegrates and 
yields a series of radioactive products. The first one is 
moderately radioactive, and is called mesothorium. Being 
cheaper than radium, mesothorium is sometimes used as a 
substitute, although it lasts only a few years. Actinium 
and polonium are very rare radioactive elements. 

625. The constitution of matter. — The phenomena of 
radioactivity are due to the spontaneous decomposition 
of the atoms of radium and of the other so-called radio- 
active elements. Radioactivity leads us to conclude that 
the atoms of radioactive elements are composite, unstable 
structures. Radium, thorium, etc., to be sure, behave like 
other elements in chemical changes, i.e. they participate in 
reactions which involve two or more undivided atoms each of 
which has an unvarying weight. But atoms of many radio- 
active elements spontaneously emit electrons (beta particles) 



490 PRACTICAL CHEMISTRY 

and helium atoms (alpha particles), leaving behind an 
atomic residue of less atomic weight. Many facts besides 
radioactivity, e.g. formation of ions, show that atoms and 
molecules of elements are more or less unstable. 

According to recent views of the constitution of matter, 
atoms consist of two essential parts : (i) a positively charged 
nucleus, with which the weight of the atom is associated, 
and (2) electrons {i.e. charges of negative electricity) which, 
according to most authorities, revolve around the nucleus. 
This conception of atomic structure finds an excellent il- 
lustration in the special properties of radium. 

Two other points about the constitution of matter should 
be noted. First, the number of electrons surrounding the 
nucleus of an atom of many elements has been determined. 
Thus, hydrogen is i, helium 2, oxygen 8, niton 86, 
radium 88, uranium 92. These numbers, and similar ones 
of other elements, wxre found by means of the X-ray spec- 
trum of the element. They are called atomic numbers. 

If elements are arranged in the order of their atomic numbers 
instead of their atomic weights, anomalies of the periodic classifi- 
cation disappear (402). Hence atomic numbers of the elements are 
more fundamental than their atomic weights. 

Second, experiments show that many elements readily 
lose or gain one or more electrons. Thus, radium loses 
electrons ; in fact many of the thirty or more radioactive 
elements have this property. Again, sodium chloride mole- 
cules consist of an atom each of sodium and chlorine. When 
this salt is dissolved in water, each atom forms an ion. 
Since the sodium ion is charged positively (Na+), it must 
have lost one electron, and can be represented by Na — e. 
Whereas the chlorine ion, since it is charged negatively 
(Cl~), must have gained an electron (from the sodium atom) 
and can be represented by CI + e. 




RADIUM AND RADIOACTI\'H V 491 

Finally, we must note the results of two more inves- 
tigations. First, by means of the ultra-microscope, we can 
see the motion (Brownian movement, 101 and Fig. 55) of 
particles which are minute enough to be knocked about by 
the impacts of molecules. Second, by a special electrical 
device, the paths of alpha particles {i.e. charged helium 
atoms) have been instantaneously photographed as these 
particles shoot 
through the air (Fig. 
218). In the spin- 
thariscope we see 
the result of the 
bombardment of ^. ^ ^ .u f 1 u *• 1 / u j 

Fig. 218. — Paths of alpha particles (charged 
single atoms (619). helium atoms) in moist air 

Moreover, it is pos- 
sible by means of a supersensitive electroscope to count 
charged helium atoms as they enter this instrument. 

Whatever may be our interpretation of chemical phenom- 
ena, we have little or no reason to doubt that atoms and 
molecules have been removed from the borderland of theory 
into the realm of reality. 

EXERCISES 

1. In what minerals does radium occur? 

2. Prepare a summary of (a) radium, {h) radioactivity, and 
(c) radium disintegration series. 

3. State the general properties of radium compounds. 

4. State the special properties of radium compounds. In what 
respect are they striking? 

5. Topics for home study : (a) Discovery of radium, {b) Madame 
Curie, (c) X-rays. {d) Uses of radium. {e) Properties of radium. 
(/) Ramsay and the discovery of niton, ig) Madame Curie's gram 
of radium, {h) Electrons. 

6. Discuss (a) alpha particles and {b) beta particles. Why was 
radium so named? 



492 PRACTICAL CHEMISTRY 

7. Describe (a) a spinthariscope and (b) an electroscope. What 
does each show about radium compounds? 

8. Discuss helium, niton, and the disintegration of radium as a 
connected topic. 

9. Review topics: (a) Uranium, thorium, and barium with 
special reference to radium, (b) Photography, (c) The argon family. 

10. Discuss atoms in the light of radioactivity. 

PROBLEMS 

1. Calculate the weight of radium in a milligram of (a) radium bro- 
mide, (b) radium nitrate, (c) radium sulphate. 

2. Write the formulas of the following compounds of radium : 
Iodide, fluoride, carbonate, acid carbonate, oxide, phosphate (ortho), 
sulphate, nitrate, bromide. 

3. If 2.61099 milligrams of radium bromide give 2.00988 milli- 
grams of radium chloride, what is the atomic weight of radium? (Use 
exact atomic weights of bromine and chlorine.) 



APPENDIX 

1. The Metric System of weights and measures is based on the 
meter, which is a Httle longer than a yard (i meter = 30-37 inches.) 
The unit of weight is the gram, which is about one third of an ounce 
(i ounce = 28.35 grams). A five-cent coin weighs approximately 
five grams. The unit of volume is the liter. It is slightly larger 
than a quart. 

Length. 1 meter (m.) = 10 decimeters (dm.) = 100 centimeters 
(cm.) = 1000 millimeters (mm.). Also, i decimeter = 10 centi- 
meters = 4 inches (nearly) ; and 2.54 centimeters = i inch. 

Weight. I gram (gm.) = 10 decigrams (dgm.) = 100 centigrams 
(cgm.) = 1000 milligrams (mgm.). Also, i kilogram (kg. or kgm.) 
= 1000 grams (gm.) = 2.2 lb. 

Volume. I liter (1.) = 1000 cubic centimeters (cc). Also, i cubic 
centimeter of water (at 4° C.) weighs i gram. 

2. The Thermometer used in chemistry is the centigrade. The 
boihng point of water on this thermometer is marked 100, and the 
freezing point o. The equal spaces between these points are called 
degrees. The abbreviation for centigrade is C, and for degree is °. 
Thus, the boiling point of water is 100° C. Degrees below zero are 
always designated as minus, e.g. — 12° C. means 12 degrees below zero. 



3. Weights of Gases. — The weight in grams of one liter of gases 
at 0° C. and 760 mm. is : — 



Acetylene 1.16 

Air 1.29 

Ammonia 0.77 

Carbon dioxide 1.98 

Carbon monoxide 1.25 

Chlorine 3.22 

Ethylene 1.25 

Hydrogen 0.09 



Hydrogen chloride 
Hydrogen sulphide 
Methane 
Nitric oxide . 
Nitrogen . . 
Nitrous oxide 
Oxygen . . 
Sulphur dioxide 



1.64 
1-54 
0.72 

1.34 
1.25 
1.98 
1-43 
2.93 



493 



494 



APPENDIX 



4. The Vapor Pressure of water vapor in millimeters of mercury 
is as follows : — 



Temperature 


Vapor 
Pressure 


Temperature 


Vapor 
Pressure 


Temperature 


Vapor 
Pressure 


12 


I0.5 


17 


14.4 


22 


19.7 


12.5 


I0.8 


17.5 


14.9 


22.5 


20.3 


13 


II. 2 


18 


15.4 


23 


20.9 


13-5 


II. 6 


18.5 


iS-9 


23-5 


21.5 


14 


II. 9 


19 


16.4 


24 


22.2 


14-5 


12.3 


19-5 


16.9 


24-5 


22.8 


15 


12.7 


20 


17.4 


25 


23.6 


15-5 


I3-I 


20.5 


18.0 


25-5 


24.3 


i6 


13.6 


21 


18.5 


26 


25.0 


i6.5 


14.0 


21.5 


19.1 


26.5 


25.7 



The numbers in the columns marked Vapor Pressure are the values 
for a in the formula for the reduction of gas volumes (74). 



5. Books. — Starred (*) books are primarily for teachers, though 
many parts of these books are suitable for pupils. 

1. * Alembic Club Reprints. University of Chicago Press. No. 2 
(Dalton, Atomic Theory), 3 (Cavendish, Air), 4 (Avogadro, Molecules), 
6 (Da\^, Alkalies), 7 (Priestley, Oxygen), 9 (Davy, Chlorine). 

2. Chemical Discovery and Invention in the Twentieth Century. Tilden. 
E. P. Button & Co. Modern discoveries, principles, inventions, e.g. elec- 
trons, radium, catalysis, colloids. Applications of common substances, 
especially organic compounds. Over 150 illustrations. 

3. Chemistry in America. Smith. D. Appleton & Co. Vivid story of 
chemical pioneers in our own country. 

4. Chefnistry in the Service of Man. Findlay. Longmans, Green & Co. 
Applications of modern principles to chemical industries. Cellulose, catal- 
ysis, fixation of nitrogen, colloidal state. 

5. Chemistry of Commerce. Duncan. Harper & Bros. Interpreta- 
tion of relation of chemistry to industries. 

6. Chemistry of Familiar Things. Sadtler. J. B. Lippincott Co. 

7. * Chemistry of the Radio-elements. Soddy. Longmans, Green &■ 
Co. Brief. 

8. Coal and the Coal Mines. Greene. Houghton, Mifflin Co. 

9. Colloid Chemistry. Alexander. D. Van Nostrand Co. Concise. 



APPENDIX 495 

10. Creative Chemistry. Slosson. Century Co. Cellulose, rubber, 
plastics, sugar, fats, electric furnace products. 

11. Discoveries and Inventions of the Twentieth Century. Cressy. E. P. 
Dutton & Co. 

12. * Elements of Industrial Chemistry. Rogers. D. Van Xostrand Co. 
Comprehensive (looo pages). 

13. Essays in Historical Chemistry. Thorpe. IMacmillan Co. Includes 
Boyle, Priestley, Cavendish, Lavoisier, Faraday, MendelejefT. 

14. Everyman's Chemistry. Hendrick. Harper & Bros. Useful in- 
formation interwoven in a course in general chemistry Bibliography. 

15. Famous Chemists. Tilden. E. P. Dutton & Co. Includes Boyle, 
Black, Priestley, Cavendish, Lavoisier, Davy, Dalton, Berzelius, Faraday^ 
Avogadro, Cannizzaro, Mendelejefif, Ramsay. 

16. Food and the War. Blunt and Sprague. Houghton, Mifflin Co. 
Reliable data on food, nutrition, and diet. Bibliography. Inexpensive. 

17. Food Products. Sherman. Harper & Bros. Sources, manufactur- 
ing processes, standards, pure food regulations. Bibliography. 

18. Fundamentals of Agriculture. Halligan. D. C. Heath & Co. Ferti- 
lizers, soil, insecticides, plant food. Bibliography. 

19. Handbook of CJiemistry and Physics. Chemical Rubber Co., Cleve- 
land, Ohio. Tables of physical and chemical data. 

20. History of Chemistry. Thorpe. G. P. Putnam's Son. Complete 
(400 pages). Portraits. 

21. How to Live. Fisher and Fisk. Funk & Wagnalls Co. Food, 
physiology, diet, health rules. 

22. How to Make Good Pictures. Eastman Kodak Co., Rochester, N. Y. 

23. Industrial CJiemistry. Benson. Macmillan Co. Includes water, 
fuels, iron and steel, alloys, clay products, cement, paint, cellulose, explosives. 
Condensed (420 pages). Illustrated. Bibliography. 

24. * Inorganic Chemistry. Newell. D. C. Heath & Co. Advanced 
book for reference and supplerrientary reading. 

25. * Laboratory Manual of Inorganic Chemistry. Newell. D. C. Heath 
& Co. Experiments based on No. 24. 

26. Modern Chemistry and Its Wonders. Martin. D. \'an Nostrand Co. 
Explosives, radium, electrochemistry, sugar, coal-tar, salt. Illustrated. 

27. * Nature of Matter and Electricity. Comstock and Troland. D. \\in 
Nostrand Co. Atoms, electrons, radioactivity, catalysis, constitution of 
matter. 

28. * New Era of Chemistry. Jones. D. Van Nostrand Co. Develop- 
ment of chemistry during last three decades. Catalysis, electrons, 
radioactivity. 

29. * New Knowledge {The). Duncan. H. S. Barnes & Co. Applica- 
tions of physics and chemistry. 



496 APPENDIX 

30. Non-technical Chats on Iron and Steel. Spring. F. H. Stokes Co. 

31. Outlines of Industrial Chemistry. Thorp and Lewis. Macmillan 
Co. Between No. 12 and No. 23. 

32. Photography for Students of Physics and Chemistry. Derr. Mac- 
millan Co. Principles and processes. 

SS. Radioactivity. Venable. D. C. Heath & Co. Brief. 

34. Romance of Modern Chemistry. Philip. J. B. Lippincott Co. 
Flame, fuel, explosives, extremes of temperature, crystals, agriculture. 

35. Short History of Chefnistry. Venable. D. C. Heath & Co. Concise. 

36. Some Chemical Problems of To-day. Duncan. Harper & Bros. 
Contributions to modern theoretical and industrial chemistry. 

37. Source, Chemistry, and Use of Food Products. Bailey. P. Blakis- 
ton's Son & Co. Practical information about source and manufacture of 
food. Tables. 

38. Story of Gold (The). Meade. D. Appleton & Co. Brief, non- 
technical. 

39. Story of Iron (The). Surface. D. Appleton & Co. 

40. Story of Iron and Steel (The). Smith. D. Appleton & Co. 

41. Story of Oil (The). Tower. D. Appleton & Co. 

42. Story of a Piece of Coal. Martin. D. Appleton & Co. 

43. *Study of Chemical Composition. Freund. Macmillan Co. Laws, 
history, biography. 

44. What We Eat. Hawk. Harper & Bros. Answers practical ques- 
tions about physiology, digestion, diet. 



INDEX 



Abrasive, alundum, 420 

Carborundum, 323 

Emery, 41Q 
Absolute alcohol, 297 

Temperature, 51 

Thermometer, 51 

Zero, 51 
Acetate, 299 

Ethyl, 300 
Acetic acid, 250, 298, 461 

Glacial, 298 

Ionization, 216 

Test, 300 
Acetone, 281, 298, 304 
Acetylene, 258, 272, 279, 281-283 

Burner, 282 

Flame, 281 

Oxy-flame, 282, 283 
Acid, acetic, 250, 298, 461 

Alpha-stannic, 455 

Antimonir, 355 

Calcium carbonate, 377 

Calcium sulphite, 232 

Capric, 302 

Caprylic, 302 

Carbolic, 305 

Carbonate, 255 

Carbonic, 30, 254 

Chromic, 474, 476 

Citric, 300 

Colloidal, 321 

Fluosilicic, 323 

Formic, 35 

Fruit, 299, 300 

Fuming sulphuric, 241 

Hydriodic, 343 

Hydrobromic, 341 

Hydrochloric, 136, 138 



Hydrocyanic, 371 
Hydrofluoric, 318, 322, 323, 337, 

338 
Hydrofluosilicic, ^2;^ 
Hydrogen in, 39 
Hydrosulphuric, 225 
Hypochlorous, 131- 134 
Lactic, 293, 299 
Malic, 299 
Metasilicic, 319, 321 
Muriatic, 136, 139, 156 
Nitric, 159-170 
Nitro-hydrochloric, 140 
Nitrose, 236 
Nitrosyl-sulphuric, 234 
Nitrous, 165 
Nordhausen, 241 
Oleic, 300 

Orthophosphoric, 350 
Orthosilicic, 319, 321 
Oxalic, 35, 256, 299 
Palmitic, 300 
Phosphate, 350 
Phosphoric, 347, 349, 352 
Prussic, 371 
Pyroligneous, 298 
Salts, 231, 240, 255, 365 
Silicic, 319, 321, S2S 
Sodium carbonate, 363, 365 
Stannic, 453, 455 
Stearic, 300, 301 
Steel, 399, 401 
Sulphuric, 234-238 
Sulphurous, 68, 230 
Tartaric, 299 
Acids, 142-146 

Abnormal behavior, 213 
And metals, 142 



497 



498 



INDEX 



Acids, anhydrides, 231 

Chlorine, 145 

Common, 142 

Composition, 142 

Detection, 142 

Dibasic, 232 

Dissociation, 202 

Electrolytes, 206 

Exercises, 146 

Finding strength, 145 

Ionic definition, 204 

Ionization, 202 

Metals, 39 

Naming, 145 

Non-oxygen, 145 * 

Organic, 299-301 

Oxy, 145 

Oxygen, 145 

Problems, 147 

Properties, 142 

Reaction, 142, 206 

Strong, 216 

Tribasic, 350 

Weak, 216, 225, 365 
Actinium, 489 
Adequate diet, 311, 313 
Adhesives, 320 
Agate, 317 

Ware, 370 
Air, 102-113 

A mixture, 106 

Analysis, 107 

And burning, 18, 19 

And carbon dioxide, 29 

And combustion, 19, 20, 265 

And digestion, 309 

And gasolene, 266 

And phlogiston, 18-20 

Argon in, 107 

Blast, 265, 302, 303, 399, 429 

Burning coal, 262, 263 

Carbon dioxide in, 109 

Carbon monoxide in, 256 



Composition, 102, 107 

Constant ingredients, 106 

Currents, 65 

Drafts, 265 

Exercises, 114 

Into nitric acid, 168 

In water, 69, 106 

Liquid, 102, 106, 112 

Mixture, 105, 106 

Nitrogen in, 107 

Normal, 107 

Oxygen in, 107 

Problems, 114 

Saturated, 108 

See Atmosphere 

Test for moisture, 108 

Water vapor in, 107, 108 

Weight of liter, 493 
Airplane, 21, 266 
Airships, 47, 112 
Alchemists, aqua fortis, 163 

Aqua regia, 140 
Alcohol, 297, 298 

Absolute, 297 

And vinegar, 299 

And water, 70 « 

xAs fuel, 267, 297, 298 

B.t.u., 267 

Denatured, 297 

Ethyl, 267, 298, 300 

Fermentation, 298 

Grain, 267 

Methyl, 267, 297, 298 

Tax, 298 

Wood, 250, 267 
Alkali, 143, 303 

And hydrogen, 41, 42 

Electrolytic, 367 

Free, 303 

Metals, 360 
Alkaline reaction, 143 
Allotropy, 224 

Carbon, 244 



INDEX 



499 



AUotropy, sulphur, 224 
Alloys, 355 
Antimony 355 
Anti-friction, 356 
Bismuth, 357 
Chromium, 407, 474 
Cadmium, 357 
Copper, table, 433 
Fusible, 357 
Iron, 322 
Lead, 357 
Silicon, 322 
Silver, 466 
Steel, 407 
Table, 433 
Tin, 357, 454 
Alpha particles, 485, 487 
Path, 491 
Stannic acid, 455 
Alum, 421, 422 

And water, 60, 422 
Baking powders, 421, 365, 366 
Burnt, 421 
Chrome, 421, 476 
Hydrolysis, 421 
Iron, 421 
Potassium, 421 
Water purification, 60, 422 
Alumina, 419 
Aluminates, 417, 420 
Aluminium, 415-424 

Acetate, 422 

Alloys, 418 

And sodium hydroxide, 41, 42, 417 

Bronze, 418, 433 

Chloride, 417, 420 

Cleaning by, 466 

Extruded, 416 

Family, 332 

Hydroxide, 420, 421, 422 

In cleaning silver, 466 

In steel making, 399, 403, 4^7 

Manufacture, 415 



Metal, 420 
Non-metal, 420 
Oxide, 324, ,41 5, 418-420 
Properties, 416 
Salts, hydrolysis, 421 
Sulphate, 420, 421 
Test, 420 

Uses, 417 
\lumino-thcrmic method, 418, 419 
\lundum, 420 
Amalgams, 447, 464 

Gold, 470 
Amethyst, 316 
Ammonia, 148-157 

And chlorine, 151, 153 

And magnesium, 151 

And water, 151 

Anhydrous, 150 

Catalyst, 104, 153 

Chemical conduct, 150 

Composition, 153 

Decomposition, 151 

Formation, 45, 148 

Formula, 198 

Fountain, 150 

Into nitric acid, 169 

Liquefied, 150 

Liquid, 150 

Manufacture, 152 

Muriate of, 156 

Preparation, 148 

Problems, 157 

Properties, 150 

Refrigerant, 154 

Soda process, 363 

Softening by, 386 

Solubility, 150 

Synthesis, 151 

Synthetic, 153 

Term, 148 

Test, 151 

Volumetric composition, 153 

Water, 148, 150 



500 



INDEX 



Ammonia, weij^ht of liter, 150, 493 
Ammoniacal liquor, 149, 277 
Ammonium, 155 

As metal, 155, 214, 215 

Carbonate, 157 

Chloride, 103, 105, 150, 156 

Compounds, 155, 156 

Bichromate, 103 

Ferric citrate, 412 

Hydroxide, 148-150, 155 

Magnesium phosphate, 442 

Molybdate, 350, 480 

Nickel sulphate, 479 

Nitrate, 156, 165 

Nitrite, 103 

Oxalate, 386 

Phospho molybdate, 350 

Sulphate, 105, 156, 239 

Stannate, 455 

Test, 156 
Amorphous, 223, 247 

Carbon, 247 

Sulphur, 223 
Amyl acetate, 300 

Valerate, 300 
Anatysis, water, 79 
Anaesthetic, 166, 304 
Anglesite, 456 
Anhydride, 68, 231 

Acid, 399 

Carbonic, 255 

Phosphoric, 350 

Silicic, 321 

Sulphuric, 233 

Sulphurous, 231 
Anhydrite, 384 
Anhydrous, 74 

Copper sulphate, 434 
Animal charcoal, 250 
Anions, 202, 209, 215 
Annealing glass, 327 
Anode, 209, 367, 368, 387, 416, 430, 
431, 439 



Anthracene, 305 
Anthracite coal, 248 
Antichlor, 135, 232 
Antimonic acid, 355 
Antimony, 355, 356 

Alloys, 355 

Oxy chloride, 356 

Sulphide, 225, 355 

Test, 356 

Trichloride, 355) 35^ 

Trioxide, 355 

Trisulphide, 356 
Antimonyl, 356 
Antiseptic, 304, 305 
Apatite, 337 
Apparatus, aluminium, 415 

Blast furnace, 392, 393, 427-429 

Bromine, 340 

Burning hydrogen, 44 

Carbon dioxide, 28 

Coal gas, 276 

Collecting hydrogen, 41 

Composition of air, 107 

Composition of ammonia, 153 

Contact acid, 237 

Converter, 398, 400, 430 

Copper sulphide ores, 427 

Distillation, 62 

Electrolysis of salt, 129 

Electrolysis of water, 78 

Four-ply paper, 320 

Gasolene, 270 

Glass making, 325, 326 

Hydrochloric acid, 136 

Hydrogen, 40 

Ice, 154 

Ionization, 206 

Kipp, 40 

Lavoisier's, 19 

Liter of oxygen, 55, 56 

Magnesium, 439 

Morley's, 80 

Nitric acid, 159, 160, 168, 169 



INDEX 



501 



Apparatus, oxygen, 14 

Oxyj^cn in water, 78 

Oxygen rescue, 21, 22 

Petroleum, 379 

Rescue, 21, 22 

Silica, 318 

Sodium hydroxide, 367, 368 

Sulphuric acid, 235, 237 

Vapor pressure, 65, 66 

Water, 81, 82 

Water gas, 274 
Aqua fort is, 163 
Aqua regia, 139, 355, 356, 357 

Dissolves gold, 472 

Nitric acid, 162 
Argol, 299 
Argon, no, $3^, 44o 

And nitrogen, 107, in 

Family, 332 

In air, 107 

iMonatomic, 179 

Name, no 

Preparation, in 

Properties, no 
Arrhcnius, 201, 202 
Arsenic, 354, 355 

Sulphide, 225, 355 

WTiite, 354 
Arsenious oxide, 354 
Arsenopyrite, 354 
Arsine, 356 
Asbestos, 319 
Asphalt base, 271 
Atmosphere, 102 

Carbon dioxide, 31 

Deliquescence, 75 

Efflorescence, 74 

Nitrogen, 104 

Rare gases, in 
Atmospheric pressure, 52 

And boiling point, 67 

Normal, 67 
Atomic number, 490 



Atomic theory, 89 

And chemical change, 91, 92 
Conservation of matter, 92 
Constant composition, 92 
Exercises, 94 
Multiple proportions, 93 

Atomic weights, 93, 182-190 
Accurate, 187 

And equivalent weights, 186 
And molecular weights, 179 
And periodic classification, 331, 

333 
And properties, 334 
Approximate, 94, 182, 184 
Atomic numbers, 490 
Determination, 182, 183, 189 
Dulong and Petit, 185 
Exercises, 190 

From molecular weights, 182 
How found, 182, 183 
International, 188 
Learning, 335 
Oxygen, 94 

Problems, 190, 191, 228 
Radium series, 488 
Ratio in molecule, 100 
Relative, 94 
Specific heat, 185 
Standard, 94 

Summary, 189 

Symbols, 97 

Table, Back cover 
Atoms, 89, 90 

And ions, 202 

And molecules, 90, 91 

Combining capacity, 193 

Constitution, 490 

Groups, 143, 193 

In molecule, 174, i75^ 222, 348, 354 

Nucleus, 490 

Real, 489-491 

Review, 182 

Same as molecules, 179 



502 



INDEX 



Atoms, small, 94 

Symbols, 96, back cover 

Unstable, 489, 490 

Valence, 198 

Weight of single, 183 
Auric chloride, 472 
Automobile, 266 

Carbon monoxide, 34 

Reflector, 292, 467 

Tail lights, 324 

Tires, 218 
Avogadro, 172 

Theory, 172, 174 
Azote, 104 
Azurite, 426, 435 

Babbit metal, 356 
Bacteria, nodules, 105 

Water, 61 
Baking powder, 30, 365 

Alum, 421 

Ingredients, 157 

Phosphate, 350 

Tartrate, 366, 374 
Baking soda, 299, 365 
Balancing equations, 116 
Balard, 340 
Balloons, 47, 112 
Barite, 240 
Barium, 388 

Chloride, 74, 388 

Chromate, 388 

Nitrate, 388 

Sulphate, 240, 338, 460 

Test, 388 
Barometer, 53 

Height, 53 

Normal, 53 

Reading, 53 
Barytes, 240, 388 
Base, 142-146 

Ammonium hydroxide, 148 

Ionic definition, 204 



Bases, 142-146 

Abnormal behavior, 213 

Composition, 143 

Electrolytes, 206 

Exercises, 146 

Ionization, 202 

Names, 146 

Naming, 145 

Problems, 147 

Properties, 143 

Strong, 216, 365 

Weak, 216, 365 
Basic reaction, 143 

Salt, 454 

Steel, 401 
Battery, dry, 477 
Bauxite, 415 
Becquerel, 482 
Beet sugar, 280, 290 
Bell metal, 433 
Benzene, 272, 279, 305 
Benzine, 268, 271 
Ber>'l, 319 
Berzelius, 96 
Bessemer process, 398-401 

Steel, 398-401 

Thomas-Gilchrist, 401 
Beta particles. 486, 489 
Beta-stannic acid, 453 
Beverage, charged, 69 
Bicarbonate, 255 
Bichromates, 475 
Bismite, 356 
Bismuth, 356-358, 458 
Alloys, 357 
Basic chloride, 358 
Test, 358 
Bismuthinite, 356 
Bittern, 340 
Bituminous coal, 248 
Bivalent element, 193 
Black, 254 
Damp, 273 



INDEX 



503 



Black, lead, 246, 456 
Blast furnace, 392 
Copper, 427, 428 
Lead, 456 
Blast lamp, 48, 265 
Bleaching, 1 33-1 35 
Apparatus, 135 
Chlorine, 133- 1 35 
Fruits, 232 

Hydrogen peroxide, 84 
Nuts, 232 
Ozone, 22 
Powder, i33-i35 
Process, 134, 135 
Sodium peroxide, 371 
Straw, 233 

Sulphurous acid, 232, 233 
Vegetables, 232 
Block tin, 62, 452 
Blood, 20 

Carbon monoxide, 33 
Iron in, 391 
Blooms, 396 
Blowpipe flame, 286 
Acetylene, 282, 283 
Glass, 325 
Mouth, 286 
Oxy-hydrogen, 47 
Blue print, 412 
Blue, Prussian, 413 
Blue stone, 240, 435 
Blue vitriol, 434 
Bluing, 412 
Body, elements in, 8 
Boiling point, 64, 67 
Abnormal, 213 
Normal, 67 
Raising, 213 
Water, 64, 67 
Bomb calorimeter, 262 
Bornite, 391, 426 
Boneblack, 250, 290 
Bones, 346, 350 



Books, list, 494-496 
Borax, 369, 370 
Bead, 370, 476 
Hydrolysis, 370 
Softening by, 386 
Bordeaux mixture. 434 
Boron family, 332 

Oxide, 324 
Boyle, 53, 54 

Law, 53, 55, 57, 58 
Brass, 433 
Bread, 28, 294, 295 

And carbon dioxide, 28, 294, 295, 

365, 366 
Composition, 308 
Breathing, 20 
Oxygen, 21 

Oxygen apparatus, 21, 22 
Bricks, 424 
Brimstone, 219 
Brine, 136 
Ice, 154 
Britannia metal, 356, 454 
British thermal unit, 261 
Charcoal, 265 
Coal gas, 276 
Coke, 261, 265 
Fuel gases, 261 
Fuel oil, 261, 266 
Natural gas, 274 
Producer gas, 274 
Soft coal, 261 
Water gas, 275 
W'ood, 265 
Bromides, 339, 341 
Bromine, 339-341 

Molecular formula, 179 
Water, 341 
Bronze, 433 

Aluminium, 418, 433 
Brownian movement, 91, 491 
B.t.u., 261 
Problems, 288 



504 INDEX 

B.t.u., see British thermal unit 
Bullets, 459 
Bunsen, 284 

Burner, 275, 283, 284 

Flame, 284, 285 
Burettes, 144-145 
Burner, acetylene, 282 

Bunsen, 275, 283, 284 

Gas stove, 275 

Oil, 266 
Burning, 17-19 

Coal, 262, 263 

Equations, 264 

Wood, 265 
Butane, 272 
Butter, 302 
Butyrin, 302 



Cadmium, 446 

Alloy, 357, 446 

Atom in molecule, 179 

Test, 446 
Calcite, 376 
Calcium, 376, 387 

Acid carbonate, 377 

Acid sulphite, 232 

And hard water, 385 

Borate, 369 

Carbide, 198, 257 

Carbonate, 28, 124, 125, 139, 178, 

255, 364, 376-379 
Chloride, 75, 108, 386 
Compounds, 386, 388, 389 
Cyanamide, 104, 105, 387 
Family, 332 
Fluoride, 337, 338 
Hydrogen and, 40 
Hydroxide, 70, 133, 198, 379, 

381 
Light, 47 
Nitrate, 105, 386 
Nitride, 387 
Oxide, 257, 379-381 



Oxalate, 386 

Phosphate, 250, 325, 346, 347, 350, 
352 

Silicate, 324, 347 

Sulphate, 218, 219, 240, 384 

Sulphide, 386 

Test, 386 
Calculation, equations, 121 

Gravimetric, 121- 125 

Volume from weight, 123 
Caliche, 371 
Calomel, 448 
Calorie, 261 

Food, 310 

In food servings, 312, 313 

Large, 261 

Small, 261 
Calorimeter, 262, 310 
Candle flame, 279, 281 

Power, 279 
Candles, 270 
Candy, 289, 295 
Cane sugar, 289-293 
Cannizzaro, 185 
Capric acid, 302 
Caprylic acid, 302 
Caramel, 290 
Carat, diamond, 245 

Gold, 471 

International, 245 
Carbides, 252 

Calcium, 252, 257 

Silicon, 252, 322 
Carbohydrates, 289 

Food, 307, 309, 311-313 

Quantity needed, 311 
Carbolic acid, 305 
Carbon, 25-35, 244-252 

Allotropic, 244 

Amorphous, 244, 247 

As fuel, 260, 262-265 

Atomic weight, 184 

Chemical conduct, 252 



INDEX 



505 



Carbon, compounds, 25-35, 252-258, 
289-305 
Crystalline, 244 
Cycle, 32 
Diamond, 244 
Bisulphide, 226, 227 
Electric light, 251 
Exercises, 37 
Family, $3^ 

Finding atomic weight, 183 
Gas, 247, 251 
In fuels, 260 
In iron, 395, 397 
Minimum weight, 183 
Occurrence, 25 
Oxides, 26, 34, 35, 36, 37, 88, 89, 

97. 393 
Problems, 258, 259 
Reduction by, 252, 394 
Test, 250 

Tetrachloride, 135, 305, 341 
Carbon dioxide, 26-33, 252-255, 461 
And bread, 28, 294, 295, 365, 366 
And combustion, 252 
And life, 253, 254 
And weathering, 319 
Atmosphere, 31 
By fermentation, 253 
By oxidation, 253 
Chemical conduct, 30 
Choke damp, 273 
Decay, 27 

Detection in air, no 
Discovery, 254 
Experiments, 28 
Extension, 252-255 
Fire extinguisher, 28, 32, 33 
Formation, 26 
In air, 109, no 
In breath, 27 
Liquid, 30 

Life, 30, 31, 253, 254 
Manufacture, 28 



Mole, 176 

Molecular weight, 172, 173, 174 

Not poisonous, 30 

Plants, 31 

Preparation, 28, 253 

Problems, 38, 259 

Properties, 29, 253 

Review, 252-255 

Solid, 30 

Test, 27, 30, no, 253, 382 

Vapor density, 173 

Weight of liter, 29, 253, 493 
Carbon monoxide, 33-35, 198, 256, 
283, 393 

In gases, 274 

In illuminating gas, ^^, 278 

Mole, 176 

Poisonous, s^, 256 

Preparation, 35, 256 

Properties, S3, 257 

Reducing agent, 34 

Reduction by, 256 

Review, 256 

Test, 257 

Weight of liter, 33, 493 
Carbona, 135, 305 
Carbonates, 255 

Acid, 255 

Acid calcium, 255 

Normal, 255 

Normal calcium, 255 
Carbonated water, 29 
Carbonic acid, 30, 254, 319, 365 

Anhydride, 255 

Ions, 254 
Carborundum, 252, 322, 323 
Carboy, 139 
Carburetor, 275 
Carnallite, 372, 439 
Carnelian, 317 
Carnotite, 482 
Casein, 293 
Cassiterite, 452 



5o6 



INDEX 



Cast iron, 395 
Catalysis, 45, io4, 233 
Enzymes, 295 
Sulphur trioxide, 233 
See Catalyst 
Catalyst, 45, 153 
Ammonia, 104 
Iron oxide, 237 
Nitric oxide, 235 
Platinum, 237 
Poisoning, 238 
Cathode, 209, 367, 368, 387, 416, 439 
Cations, 202, 209 

List, 215 
Caustic, 366 
Lime, 379 
Potash, 373^ 374 
Soda, 366 
Caves, 255, 377 
Cavendish, iii 
Cell, diaphragm, 367 
Electric, 436 
Non-diaphragm, 368 
Celluloid, 296 

Cellulose, 232, 265, 289, 295-297 
Derivatives, 296 
Fiber board, 446 
Nitrates, 296 
Cement, 382-384 
Portland, 384 
Zinc, 446 
Cementite, 395 

Centigrade thermometer, 51, 493 
Cerium, 480 
Oxide, 286 
Cerussite, 456 
Chalcedony, 317 
Chalcocite, 218, 426 
Chalcopyrite, 218, 391, 426 
Chalk, 378 

Precipitated, 379 
Change, chemical, i, 2, 5, 9, 14, 16 
17, 41, 42, 89, 91, 115, 309 



Electrochemical, 436 

Physical, 65 
Charcoal, 247, 249 

Animal, 250 

Burning, 265 

In gunpowder, 373 

Sugar, 290 

Uses, 249 

Wood, 249, 250 
Charles' law, 51, 52, 55, 57 
Checkerwork, 401 
Cheese, 293 
Chemical change, i, 2 

And equation, 115 

And oxygen, 16 

Atoms, 89 

Attraction, 6 

Characteristics, 2, 3 

Compounds, 5-10, 35-37, 77-83, 
88, 89, 91-93, 96-100, 121-125 

Elements, 5-10 

Hydrogen, 41 

In body, 309 

Interpretation, 91 

iSIercury oxide, 5 

Other names, 9 

Oxidation, 17 

Potassium chlorate, 14 

Substitution, 42 
Chemical conduct. 2 
Chemical engine, 32 
Chemistry, i 

Organic, 25, 198, 289 
Chile saltpeter, 341, 342, 370, 371 
China ware, 423 
Chinese white, 445 
Chloride, 132, 140 

Aqua regia, 140 

Composition, 143 

From hydrochloric acid, 139 

Hydrogen, 132 

Insoluble, 140 

Ions, 202, 203, 207 



INDEX 



507 



Chloride, lime, 133 

Names, 140 

Preparation, 139 

Properties, 140 

Sulphur, 218 

Test, 140 
Chlorinator, 61 
Chlorine, 129-135 

Acids, 145 

And ammonia, 151 

And bromides. 340 

And hydrogen, 45, 132, 138, 180 

And water, 61 

Atomic weight, 184, 188 

Atoms in molecule, 175 

Bleaching, i33-i35» 232 

By electrolysis, 129, 130, 366-369 

Chemical conduct, 132 

Compounds, 61 

Discover>', 130 

Electrolytic, 368, 369 

Equivalent weight, 186 

Exercises, 141 

In World War, 131 

Ion, 490 

Liquid, 61, 131 

Nascent, 139, 140 

Occurrence, 129 

Preparation, 129, 130 

Problems, 141 

Properties, 130 

Purification by, 61 

Salts from acids, 146 

Uses, 135 

Water, 77, 78, 131 
Chloroform, 304 
Chlorophyll, 31, 391 
Choke damp, 273 
Chromates, 474, 475 

Ions, 475 

Lead, 462 
Chrome alum, 476 

Iron ore, 474 



Steel, 404, 407, 474 
Yellow, 475 
Chromel, 474 
Chromic acid, 474, 476 
Anhydride, 474 
Oxide, 476 
Chromite, 474 
Chromites, 476 
Chromium, 474-476 
Alloys, 474 
Family, 333 
Hydroxide, 476 
Ions, 475 
Oxide, 418 
Steel, 404, 407, 474 
Test, 475 
Thermit, 418 
Trioxide, 474, 476 
Cinnabar, 218, 446, 449 
Citric acid, 300 
Classification, elements, 329-336 

Periodic, 33o-33(^ 
Clay, 246, 319, 383, 415, 422 
Filler, 297 
Products^ 423 
Climate, 65 
Clinker, 384 
Clouds, 59, 65, 107 
Coal, anthracite, 248 
Beds, 248 
Brown, 248 
Burning, 262, 263 
Bituminous, 248, 250, 272 
Composition, 248 
Fire, 34, 35, 263-265 
Formation, 248 
Fossil, 249 

Gas, 149, 264, 272, 275-279 
Hard, 248, 263 
Microscopic section, 249 
Soft, 18, 248, 250, 261 
Sulphur in, 219 
Tar, 277, 278, 305 



5o8 



INDEX 



Coal, varieties, 247 

Water gas from, 275 
Cobalt, 480 

Nitrate, 420, 446, 480 

Potassium nitrite, 480 

Test, 480 
Cocoanut oil, 302 
Coke, 247, 250, 261, 265, 323, 392 

Blast furnace, 34, 392, 393 

Ovens, 149, 251 

Petroleum, 271 

Products, 251 
Cold storage, 154 
Colemanite, 369 
Collodion, 296 
Colloid, 77 

Gold, 472 

Graphite, 246 

Particles, 91 

Silicic acid, 321 

Solution, 76, 77, 90, 91 

State, 76 

Suspension, 76, 294 
Combination, 16, 91 

Oxygen, 15 
Combining numbers, 186 

Weights, 186 
Combustion, 17, 26 

Ammonia, 151 

And carbon dioxide, 30 

And air, 19 

And oxygen, 20 

Broad meaning, 45, 132 

Fuels, 264 

Oxidation, 17 

Products, 263 

Spontaneous, 18 
Common salt, 362 
Composition, ammonia, 153 

And formulas, 97, 98 

Constant, 6, 88, 92 

Carbon oxides, 36 

Gravimetric, 6, 36, 79, 80, 98-100 



Ocean, 8 
Per cent, 99 
Percentage, 99 

Volumetric, 79, 81, 138, 153, 179, 
180 
Compound, 6 
And elements, 9 
Carbon oxides, 35 

Formula, 9, 96-100, 121, 122, 177, 
178 

Percentage composition, 99 

See Chemical compound 
Concentration, ore, 427 
Concentrated solution, 69 
Concrete, 383 

Reenforced, 383 
Condenser, coal gas, 276 ^ 

Water, 62 
Cones, Bunsen flame, 285 
Conservation of matter, 3, 10, 87, 92 

Atomic theory, 92 

Law, 3, 10, 87, 92, 121 
Constant composition, 6, 88, 92 

Air, 106 

And mixture, 106 

Atomic theory, 92 

Carbon oxides, 36 

Law, 6, 88 
Converter, copper, 429, 430 

Iron, 395, 398-401 
Cooking, 28, 30 

Soda, 30, 365 
Copper, 426-435 

Alloys, 433 

And nitric acid, 163 

And sulphuric acid, 229, 239 

Anodes, 430, 431 

Blister, 430 

Carbonates, 426 

Chemical change, 91 

Converter, 429, 430 

Cupric compounds, 434 

Cuprous compounds, 433, 434 



INDEX 



509 



Copper, displacement, 432 
Electric cell, 436, 437 
Electrolysis, 211, 43° 
Electrolytic, 431 
Eamily, 332 
Ferrocyanidc, 433 
Flame test, 432, 433 
Flotation, 428 
Ions, 431, 434, 436 
Matte, 428, 429 
Metallurg>% 426-430 
Nitrate, 435 
Oxide, 46, 252, 432 
Paris green, 355 
Poisonous compounds, 434 
Refining, 430 
Sulphate, 73, 74, 98, 211, 239, 240 

431, 434 

Sulphide, 218, 426-430 

Smelting, 428 

Test, 370, 433 

Uses, 433 
Copperas, 240, 411 
Coquina, 378 
Coral, 379 
Cordite, 303, 304 
Corrosive sublimate, 449 
Corundum, 415, 419, 420 
Cotton, 295 

Gun, 296 
Cottonseed oil, 301, 302 
Courtois, 341 
Crisco, 302 

Cream of tartar, 299, 366, 374 
Crocus, 410 
Crucible, 246 

Steel, 404, 405 
Cr>'olite, 325, 337, 415 
Crystallization, 71, 72 
Efflorescence, 74 
Water of, 73, 74 
Cn,'stals, 71-74 
Ice, 63, 64 



CuUinan diamond, 245 

Cupel, 457 

Cupric oxide, 434, 435 

See Copper 

Sulphate, 434 

Sulphide, 435 
Cuprite, 426, 434 . 
Cuprous compounds, 433, 434 

Oxide, 292, 434 
Curie, 482, 483 
Cutting metals, 283 
Cyanamide, calcium, 105, 387 
Cyanide process, 470 
Cyanogen iron compounds, 412 
Cycle, carbon, 32 

Oxygen, 32 

Phosphorus, 351 

Daguerre, 469 
Dalton, 89 
Dampers, 264 
Davy, 273 

Chlorine, 130 

Iodine, 342 

Lamp, 273 

Nitrous oxide, 166 

Sodium, 360 
Decay, 27 
Decomposition, 14 

Double, 144 

Potassium chlorate, 14 
Decrepitation, 363 
Definite proportions, 88 

Law, 88 

See Constant composition 
Deflagration, 163 
Dehydrated, 74 
Deliquescence, 75 

Vapor pressure, 75 
Denatured alcohol, 297 
Deoxidizing agent, 417, 418 
Desiccator, 75 
Developer, 468 



5IO 



INDEX 



Dew, 59, 107, iGo 

Point, 108 
Dewar flask, 112, 292 
Dextrin, 294, 295 
Dextrose, 291, 292, 294 

Test, 292 
Diamond, 244 

And carborundum, 323 

Carat, 245 

Cullinan, 245 

Drill, 25, 245 

Uses, 25 
Diastase, 293, 295, 298 
Diatoms, 317 
Diatomaceous earth, 317 
Dibasic acid, 232 
Dichromate, 475 

Ions, 475 
Diet, adequate, 311, 313 
Diffusion, 43 

Gases, 57 

Hydrogen, 43 
Digestion, 27, 309 

Products, 27 
Dilute solution, 69 
Disinfectant, carbolic acid, 305 

Chlorine, 135 

Formaldehyde, 304 

Phenol, 305 
Displacement, 42 

And valence, 196 

Interpretation, 436 

Metal and acid, 42 

Metals, 432, 435 

Series, 435 
Dissociation, 202-216 

Acids, bases, salts, 202-216 

Degree of, ions, 215 

Electrolytic, 205, 206 

Ionization, 202-216 

See Ions 
Distillate, 62 
Distillation, 62 



Alcohol, 298 

Dry, 250 

Fractional, 268 

Water, 62 

Wood, 298 
Distilled water, 62, 63 
Divalent element, 193, 195 
Dolomite, 439, 442 

Lining, 401 
Double decomposition, 144 
Dough, 28, 30, 294, 295, 365, 366 
Drying, 65 
Dulong, 185 
Dulong and Petit, 185 
Dumas, 80 
Duralumin, 418 
Duriron, 322 

Dutch process, paint, 461 
Dyad, 193, 195 
Dyeing, 422 
Dyes, 422 
Dynamite, 303, 3 iQ 

Earthenware, 424 
Effervescence, 69 
Efflorescence, 74 
Eggs, 219 

Decayed, 224 

Preserving, 320 

Sulphur in, 226 
Electric cell, 436 
Electric charge, ions, 214, 215 

Valence, 215 
Electric furnace, 247 

Calcium carbide, 257 

Carbon disulphide, 227 

Carborundum, 323 

Graphite, 247 

Phosphorus, 346 

Steel, 405 
Electrical energy, 437 
Electricity, attraction. 209 

Kinds, 209 



INDEX 



51 



Electricity, minus, 209 

Plus, 2og 
Electrochemical change, 436 

Series, 436 
Electrodes, 25, 209, 247 
Electrolysis, 206, 208-212 

Applications, 212 

Calcium chloride, 387 

Carnallite, 354 

Copper sulphate, 211, 305, 431 

Example, 209 

Fluorine, 337 

Gold, 315 

Hydrochloric acid, 209 

Illustrations, 148, 209 

Interpretation, 148, 212 

Ionic interpretation, 208, 209 

Lead, 369 

Migration, 212 

Secondary products, 210 

Sodium chloride, 73, 129, 130, 293 
366 

Sodium hydroxide, 210, 211 

Water, 78, 211 
Electrolytes, 136, 148, 204, 205 

Boiling point, 139 

Chemical behavior, 140 

Examples, 206 

Freezing point, 139 

Molecular weight, 214 
Electrolytic cell, 148 

Dissociation, 137 

Solutions, 213 
Electromotive series, 437 
Electrons, 486, 488, 489, 490 

And ions, 490 

Around nucleus, 490 

Change of, 490 
Electroplating, 212 

Gold, 472 
Silver, 467 
Electroscope, 484, 485, 491 
Electro-silicon, 318 



Elcctrotyping, 212, 246 
Elements, 6 
AUotropic, 224, 244 
And atomic weights, 97, 182-190, 

330, 333 
And compounds, 9 
Bivalent, 193, 195 

Chemical change, 9 

Chemically equivalent, 186 

Classification, 329-336 

Distribution, 7, 8 

Divalent, 193, 195 

Electrons, 490 

Eciuivalent weight, 185 

Families, ^32 

Gaseous, 179 

Groups, 332 

Halogen, 332, 333 

Hexavalent, 193 

Human body, 8 

In body, 8, 218 

Inert, 87, 104, no, iii 

Ions, table, 214 

Isotopic, 488 

Latin name, 9 

Molecular formulas, 123, 179 

Molecular weights, 123 

Molecules, 90 

Monatomic, 179 

Negative, 409 

Number, 7 

Oxides, 17 

Pentavalent, 193, 195 

Periodic classification, 330-336 

Positive, 410 

Quadrivalent, 193, 195 

Quinquivalent, 193, 195 

Radioactive, 489 

Symbols, 8, 97 

Table, 7, Back cover. 

Tetravalent, 193, 195 

Trivalent, 193, 195 
Univalent, 193, 195 



512 



INDEX 



Elements, valence, 193-195. 2>2>^ 
Emery, 331, 415, 419 
Emulsion, 76, 77 

Soap, 304 
Enamel, 370 
Energy, chemical, 437 

Electrical, 437 

From food, 218, 307, 309 

Heat, 261 
Engine, gasolene, 266 
Enzymes, 196, 216, 295 

Zymase, 298 
Epsom salts, 240, 356, 441 
Equation, 9, 10, 11 5- 126 

Arrow in, 119, 152 

Balanced, 121 

Balancing, 116 

Calculations, 121 

Exercises, 141, 157, 170 

Factors, 115 

For reactions, 125 

Gas, 180 

Gaseous, 151 

Gravimetric, 120, 121, 180 

Ionic, 141, 205, 207, 368 

Molecular, 179, 180 

Not algebraic, 119 

Preliminary, 9, 10, 115 

Problems, 147, 158 

Products, 115 

Quantitative, 121 

Reading, 10, 119 

Reading reversible, 152 

Reversible, 152 

Signs, 119 

Steps in writing, 116 

Symbols, 115 

Terms, 119 

Thermal, 261, 262 

Thermo-chemical, 262 

Verbal, 9 

Volume and weight, 1 23 

Volumetric, 180 



Writing, 11 5- 119 
Equilibrium, 152 
Ammonia, 152 
Completion, 152 
Equivalents, 186 
Equivalent weights, 185-187 
And atomic weights, 186 
Element, 185 
Exercises, 190, 199 
Finding, 186 
Table, 187 
Esters, 207, 300, 302 

Fats, 208 
Etching, 268, 338, 339 
Ethane, 184, 272 
Ether, 214, 304 

And water, 43, 70 
Ethyl, 300 

Acetate, 207, 300 
Alcohol, 267, 298, 300 
Butyrate, 300 
Ether, 214, 304 
Radical, 300 
Ethylene, 172, 241, 272, 278, 391 
Eudiometer, 81 
Evaporation, 65, 107 

From body, 109 
Exercises, acids, 146 
Air, 114 
Alcohols, 306 
Alloys, 462 
Aluminium, 424 
Ammonia, 157 
Atomic weights, 190 
Bases, 146 

Calcium compounds, 388 
Carbon, 37, 258 
Carbon oxides, 38, 258 
Chemical change, 10 
Chlorine, 141 
Chromium, 480 
Composition, loi 
Compounds, 10 



INDEX 



513 



Exercises, copper, 437 
Electrolysis, 217 
Elements, 10 
Equations, 126, 141, i57> 170. 228, 

414 
Equivalent weights, iqo, 199 
Fats and soap, joO 
Food, 314 
Formulas, 100, 180 
Fuel, 287 
Fuel value, 314 
Gases, 57 
Glass, 328 
Gold and silver, 472 
Halogens, 344 

Home study, 23, 48, 58, 85, ii4: 
141, 157, 217, 242, 258, 288, 344: 
375, 389, 414, 424, 437, 450, 462 
Hydrocarbons, 287 
Hydrochloric acid, 141 
Illuminants, 287 
Ions, 217 

Iron compounds, 413 
Lead, 462 

Magnesium, 450 

Manganese, 480 

Menus, 314 

Mercury, 450 

Metals, 336 

Mole, 180 

Molecular weight, loi 

Molecular weights, 180 

Molecules, 180 

Neutralization, 217 

Nitric acid, 170 

Nitrogen, 114 

Nitrogen oxides, 170 

Non-metals, 336 

Organic compounds, 306 

Oxygen, 23 

Periodic families, 336 

Phosphorus, 358 

Potassium compounds, 375 



Practical topics, 414, 450, 4O2 

Radium, 491 

Reaction?, 126 

Review, 344, 389, 414 

Salts, 146 

Silicon, 327 

Sodium comjiounds, 374 

Sugars, 305 

Sulphates, 242 

Suli)hides, 228 

Sulphur, 227 

Sulphuric acid, 241 

Sulphur oxides, 241 

Symbols, 100 

Tin, 462 

Valence, 199 

Volume equation, 181 

Zinc, 450 
Exhauster, 276 
Explosions, coal mine, 171 

Hydrogen 40, 43 

Factors, 115 
Fahrenheit, 63 
Families, elements, 332 
Faraday, 209, 210 
Fat, 261, 300-304 

Butter, 302 

Edible, 48 

Food, 307, 309, 31 1-3 13 

Hydrogenation, 302 

Natural, 301 

Quantity needed, 311 
Fehling's solution, 292, 434 
Feldspar, 319, 422 
Fermentation, 28, 295 

Acetic, 299 

Alcoholic, 298 

Lactic, 293 
Ferric chloride, 408-413 

Compounds, 408-413 

Hydroxide, 354, 410 

Ions, 413 



SH 



INDEX 



Ferric chloride, iron, 408-413 

Oxide, 410, 418 

Sulphide, 411 

Sulphocyanate, 413 
Ferricyanides, 412, 413 
Ferrite, iron, 410 
Ferro-chrome, 474 

Manganese, 396, 399, 403 

SiHcon, 322 
Ferroso-ferric oxide, 410 
Ferrous chloride, 408-413 

Chromite, 474 

Compounds, 408-413 

Ferric oxide, 410 

Hydroxide, 410 

Ions, 413 

Iron, 408-413 

Oxide, 410 

Sulphate, 164, 165, 224,240,241.411 

Sulphide, 41 1 
Ferrocyanides, 412, 413 

Copper, 433 
Fertilizer, 105 

Artificial, 351 

Complete, 352 

Cyanamide, calcium, 105, 387 

Ingredients, 156 

Manufacture, 236 

Nitrate, 371 

Phosphate, 351, 401 

Potassium, 374, 375 

Results, 352, 353 
Fiber board, 320 
Filter paper, 295 

Water, 60 
Fire, 17 

Damp, 273 

Regulating, 264 

Extinguisher, pyrene, 135, 305 

Extinguishers, 32, 33 
Fireproof fabrics, 455, 480 
Fireworks, 218, 373 
Fixing, photography, 468 



Flame, 277-287 

Acetylene, 281 

And nitrogen, 103 

Blowpipe, 286 

Bunsen, 284 

Candle, 279-281 

Carbon monoxide, 34 

Hydrogen, 44, 47 

Lamp, 279 

Luminous, 277 

Non-luminous, 283 

Oxidizing, 285, 286 

Oxy-acetylene, 21, 282, 283 

Oxy-hydrogen, 20, 47 

Reducing, 285, 286 

Structure, 279-281, 283-286 
Flint, 317 
Flotation, 427, 428 
Flour, 294, 295 
Flower pots, 424 
Fluorescence, 486, 489 
Fluorides, 338 
Fluorine, 266, 337-339 
Fluorite, 266, 337 
Fluor spar, 266, 325, 337 
Fluosilicic acid, 255, 323 
Flux, 392 
Fog, 59, 107 
Food, 307-314 

And energy, 307, 309 

And tissue, 20 
• Baking powder, 366, 374 

Composition, 308, 309, 311-313 

Digestion, 27, 309 

Energy, 309 

Exercises, 314 

Fuel value, 261, 307, 309-313 

Function, 307 

Heat from, 310-313 

Infants, 293 

Kind needed, 313, 314 

Nitrogenous, 104, 105 

Phosphorus in, 351 



INDEX 



515 



Food, plants, 31 

Quantity needed, 311 

Salt, 363 

Servings, 312, 313 

Table, composition, 309, 311-313 

Water in, 59 
Fool's gold, 349 
Formaldehyde, 304 

Tara-, 304 
Formalin, 304 
Formic acid, 35 
Formula, 60, 97 

Air, 106 

And valence, 195-19? 

Calculation, 62 

Composition, 62, 63 

Compound, 9, 96-100, 121, 122, 

177, 178 

Expresses composition, 98, 99 

Graphic, 198 

Groups, 97 

Meaning, 97 

Molecular, 122 

Molecular weight, 61 

Molecules, 97 

Simplest, 62, 99> 100, 121, 122 
177, 178 

Structural, 198 
Formulas and symbols, 97 

Correct, 177 

Exercises, 100, 199 

From valence, 196, 197 

Salts, 197 

Structural, 198 

Writing, 97, 196, i97, i99 
Fossils, 378 

Fourdrinier machine, 297 
Franklinite, 442, 443 
Free alkali, 211 
Freezing point, abnormal, 213 

Lowering, 213 

Solutions, 212 

Water, 63 



Frost, 59, 107 
Fructose, 292 
Fruit sugar, 292 
Fuel oil, 266 
B.t.u., 266 
Burner, 266 
Plant, 270 
Separation, 272 
Fuels, 260-277 
Alcohol, 267, 298 
Combustion, 261 
Composition, 260, 261 
Exercises, 287 
Gases, 261, 273 
Hastening combustion, 264 
Heat from, 261, 262 
Heat units, 261 
Kerosene, 266 
Kinds, 260 
Liquid, 265 
Oil, 261, 266, 270, 272 
Saving, 263 
Value, 261 
Fuel value, calorimeter, 262 
Exercises, 314 
Food, 310-313 
Physiological, 310 
Fumigation, 232 
Fuming nitric acid, 167 

Sulphuric acid, 241 
Furnace, blast, 392, 427. 428, 
456 
Electric, 227, 247, 257, 346, 405 
Reverberatory, 396 
Fusible link, 285, 357 
Metals, 285 

Gain of electrons, 490 
Galena, 218, 368, 372, 456, 462 
Gallium, 335 

Galvanized iron, 358, 444 
Gamma rays, 485, 4S6, 489 
Gangue, 392 



5i6 



INDEX 



Garage, unventilated, 256 

Ventilation, 34 
Gas, 56 

Air, 104 

And pressure, 52, 53 

And temperature, 50 

Carbon, 160, 247, 251 

Carbonic acid, 254 

Coal, 149, 264, 272, 275-279 

Flame, 277, 278 

Holder, 277 

Illuminating, 278, 279 

Inert, 30, 104, no, in 

Laughing, 166 

Liquor, 149, 277 

Mantles, 185 

Marsh, 272 

Measurement, 50-55 

Natural, 39, 273 

Oil, 278 

Pintsch, 278 

Poison, 131 

Producer, 35, 39, 274 

Range, 26 

Stove burner, 275 

Volume change, 50, 52 

Water, 35, 39, 274, 275, 278 
Gases, alike, 56 

Atoms in molecule, 175 

Elementary, 118 

Formulas, 118 

Molar volume, 176, 177 

Monatomic, 179 

Nature, 56 

Solution, 69 

Theory, 57 

22.4 liters, 176, 177 

Volumetric combination, 171 

Weight of liter, 493 
Gasolene, 26, 39, 175, 266, 268 

And carbon monoxide, 35 

Boiling point, 268 

Burning, 35, 266 



Composition, 272 

Engine, 266 

Extinguishing fire, 305 

Hydrocarbons, 272 

In water, 69 

Plant, 270 

Separation, 271 
Gay-Lussac, 83 

Tower, 235, 236, 237 
Gay-Lussac's law, 82, 83, 114, 115, 
138 

x\mmonia, 153 

Atoms in molecule, 174 

Summary, 171 
Gas volumes, 50-56 

And pressure, 52 

Corrected, 55 

Finding weight, 55 

Inverse relation, 54 

Temperature, 50 
Gelatin, 457 

Blasting, 303 
Gems, 332 
Germanium, 335 
German silver, 307, 433 
Geyserite, 254, 319 
Ginger ale, 29 
Glacial acetic acid, 298 

Phosphoric acid, 278 
Glass, 2>22rT,2^, 354 

Annealing, 327 

Composition, 324 

Cut, 324 

Etching, 338, 339 

Flint, 324, 459 

Fluorescent, 377 

Green, 324 

Ingredients, 323, 324 

Kinds, 324 

Lead, 324, 459 

^Machine, 326, 327 

Manufacture, 323, 325 

Plate, 327 



INDEX 



517 



Glass, properties, 325 
Pyrex, 324 
Red, 324 
Soft, 324 
Sheet, 325, 326 
Stoppers, 318 
Water, 320 
White, 325 
Window, 325, 326 
Wire, 407 
Glauber's salt, 240, 294 
Glazing porcelain, 423 
Glover tower, 235, 236, 237 
Glucose, 292 

Test, 292, 434 
Gluten, 295 
Glycerin, 206, 300-303 

And water, 69 
Glycerol, 302 
Glyceryl, 301 
Butyrate, 302 
Oleate, 300 
Palmitate, 300 
Stearate, 300, 301 
Glycogen, 307 
Gold, 469-472 
Alloys, 472 

Auric compounds, 472 
Chloride, 470-472 
Chlorination, 470 
Coin, 472 
Colloidal, 472 
Compounds, 472 
Cyanide process, 371, 470, 471 
Electrolysis, 471 
Fool's, 349, 411 
In copper ore, 431 
In lead ore, 457 
Leaf, 471 

Metallurgy, 470, 471 
Mining, 470 
Noble metal, 140, 472 
Ore, 469 



Plating, 472 

Potassium cyanide, 472 

i'rojierties, 471 

(Hiartation, 471 

Refming, 431, 465, 47 1 

Separation from silver, 465, 471 

Sodium cyanide, 471, 472 

Solubility, 140 

Telluride, 469 

Test, 472 

Uses, 472 

Valence, 472 
Grain alcohol, 267 
Gram, 493 

Molecular volume, 175-177 

Molecular weight, 1 75-1 77, 212, 

213 
Granite, 319 
Ware, 370 
Grape sugar, 292 
Graphic formulas, 198 
Graphite, 25, 245, 246 
Artificial, 246, 247 
Colloidal, 246 
In iron, 395 
Manufactured, 247 
Occurrence, 247 
Uses, 25, 246 
Gravimetric composition, 6, 36, 79, 
80, 98-100 
Equation, 120, 121, 180 
Problems, loi 
Green fire, 388 

Glass, 324 
Grindstones, 318 
Groups, periodic, ^32 
Gun cotton, 296 

Metal, 307, 433 
Gunpowder, 218, 250, 297^ 373 
Gypsum, 219, 240, 373, 384 

Hail, 107 
Hall, 415 



5i8 



INDEX 



Halogens, 337 

Elements, 332, 333 

Exercises, 344 

Family, 266, 337 

Periodic classification, 343 
Hardness of water, 324 

Calcium compounds, 385 

Magnesium compounds, 385 
Hardness, permanent, 385 

Temporary, 385 
Hard water, 167, 324, 385 

Magnesium, 356 
Heat and condensation, 65 

And evaporation, 65 

Of neutralization, 144 
Heavy spar, 240 
Helium, 11 1 

And atomic weights, 488 

And radium, 386, 485, 487, 488 

Atoms, 485, 486, 490 

Atoms and radium, 488 

Balloons, 47 

Counting atoms, 491 

Formula, 179 

In atmosphere, 109 

Monatomic, 179 

Symbol, 179 
Helmet, oxygen, 19 
Hemaglobin, 213, 391 
Hematin, 213 
Hematite, 337, 391 
Hexad, 127, 193 
Hexane, 272 

Hexavalent element, 127 
Home study, 23, 48, 58, 85, 114, 141, 
157, 242, 258, 288, 344, 358, 375, 
389, 414, 424, 437, 450, 462 
Hornblende, 319 
Horseradish, 219 
Human body, elements, 8 

And evaporation, 109 

And water vapor, 109 

Heat, 20 



Hydrogen, 39 

Oxidation, 13, 20 

Steam engine, 20 

Temperature, 27 

Tissue, 31 

Water in, 59 
Humidity, 108 
Hydrates, 46, 74 
Hydraulic main, 276 

Mining, 470 
Hydriodic acid, 343 
Hydrobromic acid, 341 
Hydrocarbons, 26, 170, 248, 265, 268, 
271-273 

From tar, 305 

Hydrogen, 39 

In petroleum, 267, 268 

Series, 272 
Hydrochloric acid, 137, 138, 179 

And hypochlorous acid, 131, 132 

Commercial, 136 

From magnesium chloride, 442 

Electrolysis, 148, 208-209 

Exercises, 141 

Formula, 98 

Ionic test, 207 

Ionization, 210 

Ions, 209 

Manufacture, 136 

Preparation, 136 

Properties, 137 

Test, 140 
Hydrocyanic acid, 371 
Hydrofluoric acid, 267, 318, 322, 323, 

337, 338 
Hydrofluosilicic acid, 255, 318, 324 
Hydrogen, 39-48, 335, 39i 

And aluminium, 333 

And chlorine, 45, 132, 138, 180 

And combustion, 45, 46 

And electrolysis, 149, 150 

And fats, 302 

And nitric acid, 163 



INDEX 



519 



Hydrogen, and water, 44 
Apparatus, 40 
Atomic weight, 184 
Bromide, 341 
Burning, 43-45, 77 
Calculation of volume, 124 
Chemical conduct, 43-45 
Dioxide, 54, 84 
Diffusion, 43 
Displacement series, 436 
Equation, 116, 119 
Equivalent weight, 186 
Exercises, 48 
Explosion, 40, 43 
Flame, 44, 47, 77 
Fluoride, 267, 338 
Forms ammonia, 151 
From alkalies, 41 
From sodium hydroxide, 289 

From steam, 41 

From water, 40, 41, 42, 77 

Generator, 40 

In acids, 142 

In coal gas, 275, 278 

In water, 77, 81 

Iodide, 343 

Ions, 143 

Ions from acid, 204 

Iron by, 407 

Lightness, 43 

Like metals, 436 

Molecular formula, 123 

Name, 41 

Nascent, 409 

Occurrence, 39 

Peroxide, 83, 84 

Plant, 13 

Preparation, 39, 40, 41, 42 
Preparation, ecjuation, 116 
Problems, 49 
Properties, 43 
Reduces, 46 
Reduction by, 46 



I kcjHacing, 145 
Sodium and, 40 
Sulphide, 219, 224-226, 229-231, 

276, 391 
Test, 46 
Uses, 47 

Water gas, 35, 274-275 
Weight of liter, 43, 493 
Hydrogenation, 48, 302 
Hydrogen chloride, 132, 136-138, 391 
Chemical conduct, 137 
Composition, 138 
Formula, 120 
Fountain, 137, 138 
Fumes, 132, 133, 137 
Preparation, 136 
Properties, 137 
Solubility, 137 
Test, 132, 138 
Weight of liter, 137, 493 
Volume equation, 180 
Hydrolysis, 364 
Aluminium, 421 
Antimony trichloride, 284, 356 
Bismuth chloride, 286, 358 
Borax, 370 

Copper sulphate, 308, 434 
Ferric chloride, 412 
Magnesium chloride, 442 
Maltose, 198 
Potassium carbonate, 373 
Salts, 365 
Soap, 303 

Sodium carbonate, 364 
Sodium cyanide, 371 
Stannous chloride, 454 
Sugar, 195 
Hydroquinone, 468 
Hydrosulphuric acid, 225, 230 
Hydroxides, 83, 146 
Hydroxyl, 83, 143 
Groups, 14s 
Ions, 143, 211 



520 



INDEX 



Ilydroxyl, ions from base, 204 

Hypochlorous acid, 131, 134 
Chlorine water, 131 
Sodium hypochlorite, 134 

Hypo, 241, 468 

Hyposulphite, 241, 468 

Ice, 59, 63 

Machine, 154 

Manufacture, 150, 154 

Melting point, 63 

Specific gravity, 63 
Iceland spar, 376 
Illuminants, 260, 276-282 
Illuminating gas, 278-279 

Blast lamp, 48 

Candle power, 279 

Carbon monoxide, 33 

Composition, 278 

Diffusion, 57 

Flame, 277 

Luminosity, 279 
Indelible ink, 467 
Indigo, 241 

Inert gas, 30, 104, no, in 
Infusorial earth, 317, 318 
Ingots, 399, 400, 404 
Ink, 411 

Indelible, 467 

Printing, 25, 252 
Insecticides, 354, 355 
Interaction, 9 
Invar, 407 
Iodides, 343 
Iodine, 335, 341-343, 37i 

And starch, 294 

Compounds, 343 

Solution, 343 

Test, 343 

Tincture, 343 

Variable formula, 179 
Iodoform, 305, 343 
Ionic equation, 365, 368 



Ionium, 488 
Ionization, 201-216 

And concentration, 215 

Defined, 202 

Degree, 215 

Degree, table, 216 

Experiment, 206 

Interpretation, 213 

Per cent, 216 

Theory, 201, 206 
Ions, 201-216 

Acid sodium carbonate, 365 

And electrons, 490 

And molecules, 202 

And oxidation, 410 

And radicals, 202 

And reduction, 410 

And rusting, 408 

And valence, 410 

At electrodes, 210 

Atoms and molecules, 210 

Balanced sum, 203 

Charges on, 203, 214, 215 

Defined, 202 

Ferric, 413 

Ferrous, 413 

From water, 211, 212 

Hydrogen sulphide, 225 

Hydrolysis, 364 

In solutions, 213 

Kind in solution, 214 

Meaning, 209 

Migration, 210, 211 

Movement, 210 

Negative, 202, 215 

Not atoms, 202 

Phosphoric acid, 350 

Positive, 202, 215 

Representation, 203 

Sodium carbonate, 364 

Sulphuric acid, 240 

Table, 214 
I V'alence of, 215 



INDEX 



521 



Iridium, 47Q 
Iron, 301-39'^. 407-413 
And sulphuric acid, 239 
BurninR, 15 
By hydrogen, 407 
Carbon monoxide, 34 
Cast, 395 
Chlorides, 41 1 
Composition, 395, 397 
Compounds, 408-413 
Displaces copper, 432 
Disulphide, 411 
Electrolytic, 408 
Exercises, 413 
Family, 333 
Ferric, 408-413 
Ferrite, 410 
Ferrous, 408-413 
From ores, 392 
Galvanized, 444 
Hydroxides, 410 
In glass, 324 
Ions, 408, 410 
Manufacture, 392-394 
Metallurgy, 392 
Occurrence, 391 
Ore reduction, 392, 393 

Oxides, 391, 410 

Painting, 459 

Pig, 395 

Pure, 397, 407 

Pyrites, 219, 229, 391, 411 

Russia, 410 

Rust, 408 

Rusting, 398 

See Ferric 

See Ferrous 

Spiegel, 396, 399 

Sulphate, 240, 411 

Sulphide, 2, 3, 9, 10, 218, 411 

Valence, 408 

Wrought, 396-398 
Isomerism, 292 



Isomers, 292 
Isotope, 488 

Jugs, 424 

Kainitc, 372, 439 
Kaolin, 422 
Karo, 292 
Kerosene, 39, 266, 367 

And alcohol, 298 

Boiling point, 268 

Composition, 272 

Emulsion, 76 

Flashing point, 270 

Hydrocarbons, 272 

Illuminant, 268 

Lamp, 279 

Refining, 268 
Kieserite, 439 
Kiln, cement, 383 

Lime, 380, 381 

Rotary, 383 

Porcelain, 423 
Kilogram, 493 
Kinetic theory, 57 
Kipp apparatus, 40 
Krypton, iii 

Lactic acid, 293, 299 

Ferment, 293 
Lactose, 292, 293 
Lampblack, 25, 247, 251 
Lard, 301 
Large calorie, 261 
Laughing gas, 166 
Laundry, 134 
Lava, 319 

Lavoisier, 18, 19, 41, io4 
Law, 87 

Boyle's, 53, 55, 57 

Charles', 51, 52, 55, 57 

Conservation of matter, 3, 87, 121 

Constant composition, 6, 88 



522 



INDEX 



Law, definite proportions, 88 
Dulong and Petit, 185 
Exercises, 94 

Gay-Lussac, 138, 153, 171, 172, i74 
Multiple proportions, 37, 84, 88, 89 
Periodic, 334 
Specific heat, 185 
Lead, 354, 456-462 
Acetate, 299, 461 
Alloys, 356, 357, 459 
And radium, 488 
Arsenate, 355 
Atomic weight, 488 
Atomizing, 461 
Basic carbonate, 460 
Black, 246, 456 
Buckles, 461 
Carbonate, 456, 460 
Casting, 457 
Chambers, 235, 236 
Chloride, 140, 461, 462 
Chromate, 462, 475 
Desilverizing, 457 
Dioxide, 460 
Electrolysis, 457 
Fluosilicate, 457 
History, 456 

Metallurgy, 456 

Monoxide, 459 

Nitrate, 98, 458 

Oxides, 458-460 

Pencils, 25, 246 

Pipe, 458 

Plumbate, 459 

Poisonous compounds, 458 

Properties, 458 

Radio-, 488 

Radioactive, 488 

Red, 459 

Refining, 457 

Spongy, 459 

Sulphate, 456, 462 

Sulphide, 218, 226, 456, 460, 461 



Test, 461, 462 
Tetroxide, 459 
Uses, 458, 459 
White, 460, 461 
Wool, 459 
Leblanc process, 137, 363 
Leclanche batteries, 156 
Legumes, 105 
Lemonade, 300 
Levulose, 292 
Life and nitrogen, 104 
And phosphorus, 350 
Carbon dioxide, 30, 31 
Light, lime, 47, 379 

Welsbach, 286 
Lignin, 232 
Lignite, 248 
Lime, 379-381 
And water, 379 
Caustic, 379 
Chloride, 133 
Hydrated, 379, 381 
Kiln, 380, 381 
Light, 47, 379 
Manufacture, 380 
Milk of, 382 
Quick, 379 

Slaked, 133, 379, 380, 381 
Superphosphate, 352 
Sulphur spray, 218 
Water, 27, 381, 382 
Limestone, 376, 380 
Magnesium, 439 
Limonite, 391 
Lining, basic, 401, 403 
Dolomite, 401 
Magnesia, 441 
Magnesite, 442 
Link, fusible, 357 
Linolein, 301 
Liquid air, 102, 112 
Boiling, 106 
Manufacture, 113 



INDEX 



523 



Liquid air, properties, 112 
Liquids, solution, 6q 
Liquor, ammoniacal, 149 

Gas, 14Q 
Liter, gases, w'^jight, 493 
Liters, 22.4, 176, 177 
Litharge, 459 
Lithophone, 445, 460 
Litmus, 142 
Loadstone, 410 
Lockyer, 11 1 
Look boxes, 271 
Loss of electrons, 490 
Louisiana sulphur, 219 
Lubricant, 246 
Luminosity, 279 
Lungmotor, 21 

Magnalium, 418, 440 
Magnesia, 440, 442 
Alba, 442 
Calcined, 440 
Covering, 441 

Milk of, 441 
Magnesite, 439, 442 
Magnesium, 430-442 

Acid carbonate, 442 

Ammonium phosphate, 442 

Bromide, 340 

Carbonate, 439, 441, 442 

Chloride, 439, 441, 442 

Equivalent weight, 186 

Flame, 281, 440 

Hardness of water, 385 

Hydroxide, 440 

Ions, 440 

Manufacture, 439 

Minerals, 439 

Nitride, 104, 151, 440 

Oxide, 116, 120, 440 

Rocks, 439 

Sulphate, 240, 439, 441 

Test, 442 



Magnetic oxide, 410 
Magnetite, 391, 410 
Malachite, 426, 435 
Malic acid, 299 
Malt, 293 
Maltose, 293, 294 
Manganese, 476-477 
Dioxide, 324, 476, 477 
Family, ss3 

Ferro-, 396, 399, 403, 476 
Steel, 407, 476 
Sulphide, 225, 477 
Test, 477 
Manganous chloride, 477 
Mantle, Welsbach, 286, 287 
Marble, 376 
Marsh gas, 272 
Massicot, 459 
Matches, 348, 373 
Phosphorus, 15 
Matte, 428, 429 
Matter, conservation, 3, 87 

Constitution, 489 
Mendelejeff, 330, 334 
Mercuric compounds, 446, 448, 449 

Oxide, 5, 9, 19, 92, 120, 447 
Mercurous compounds, 448, 449 

Chloride, 140, 448 
Mercury, 446-450 
Alloys, 447 
Amalgams, 447 
Atom in molecule, 179 
Barometer, 53 
Bichloride, 449 
Chloride, 141, 448, 454 
Compounds, 448, 449 
Displacement, 432 
Frozen, 113 
Fulminate, 447 
In electrolytic cell, 368 
Ions, 448 
IMetallurgy, 446 
Nitrates, 449 



524 



INDEX 



Mercury, oxide, 5, 9, 19, 92, 120, 447 
Poisonous salts, 449 
Problems, 141, 45o> 45i 
Properties, 447 
Sulphide, 218, 446, 449 
Tests, 448, 449 
Thermometer, 447 
Uses, 81, 82, 447 
Valence, 448 
Mesothorium, 489 
Metal, Babbit, 356 
Bell, 433 

Britannia, 356, 454 
Gun, 433 
Monel, 433, 479 
Newton's, 357 
Noble, 140, 472 
Positive element, 410 
Rose's, 357 
Speculum, 454 
Substitution, 42 
Type, 356 
Typical, 334 
Wood's, 357 
Metallurgy, 392 
Copper, 426-430 
Gold, 470 
Iron, 392 
Lead, 456 
Silver, 464 
Tin, 453 
Zinc, 443 
Metals, 329, 330, 360 
Alkali, 360 
And acids, 142 
And non-metals, 329, 330 
And ions, 329 
And steam, 41 
And sulphuric acid, 239 
And water, 40 
Bead test, 370 
Defined, 329 
Displacement, 435 



Earth, 332 
Fusible, 357 
Rusting, 15, 408 
Table, 330 
Metaphosphoric acid, 347 
Silicic acid, 319, 321 
Stannic acid, 453 
Meteorites, 391 
Meter, gas, 277 

Metric, 493 
Methane, 184, 272, 274 
Flame, 283 
In coal gas, 275, 278 
Series, 272 
Methanol, 250 
Methyl alcohol, 250, 267 
B.t.u., 267 
Salicylate, 300 
Metric system, 493 

Problems, 11 
Mexican onyx, 377 
Mica, 319 

Migration of ions, 212 
Milk, 292 

Composition, 308 
Lactose, 292 
Of lime, 382 
Of magnesia, 441 
Sour, 299 
Sugar, 292 
Mineral matter, 308, 309 

In body, 308 
Minium, 459 
Mispickel, 354 
Mist, 59, 107 
Mixture, 4 
Air, 106 
Bordeaux, 434 
Moissan, 245, 337 
Molar volume, 176 
Molasses, 290, 298 • 
Mole, 175, 212, 213 
And boiling point, 212 



INDEX 



525 



Molf, and freezing point, 212 
Carbon dioxide, 176 
Carbon monoxide, 176 
Exercises, i8o 
Molecular weight, 176 
Nitric oxide, 176 
Problems, 181 
Oxygen, 176 
Volume, 176, 177 
Molecule, qo 
Atoms in, 174 
Chloride, 140 
Compound, 90 
Elements, 90 
Represents volume, 180 
Same as atom, 179 
Molecules and atoms, 90, 91 
And ions, 202, 203 
Atoms in, 175, 222 
Gas, 56 

Impacts of, 491 
In liquid, 90 
In solution, 213 
Real, 489-491 
Sulphur, 222 
Unstable, 490 
<^Molecular equations, 179, 180 
Molecular formula, 178 
And simplest formula, 178 
Elements, 179 
Molecular volume, gram, 176, 177 
Molecular weights, 98 

And atomic weights, 98, 179, 182, 
183 

And formula, 177, 178 

And mole, 175 

And temperature, 179 

Approximate, 173, 174 

By Avogadro's theory, 172 

By boiling point, 213 

By freezing point, 213 

By vapor density, 173, 174 

Calculation, 176 



Correct formula, 177, 178 

Determination, 174 

Electrolytes, 214 

I'Vom mole, 176, 177 

Cram, 175 

How found, 172, 173 

Insoluble substances, 174 

Non-electrolytes, 214 

Oxygen, 173 

Variable, 179 
Molybdenum, 480 

Steel, 404, 407 
Monad, 193, 195 
Monatomic elements, 179, 222 
Monazite, 480 
Monel metal, 433, 479 
Monoclinic sulphur, 223 
^Mordants, 442, 455 
Morley, 79 
Mortar, 379, 382 
Moth balls, 305 
Motor boat, 266 
Motor cycle, 266 
Mucilage, 295 
Multiple proportions, 37, 84, 88, 89 

Atomic theory, 93 
Muria, 136 

Muriatic acid, 136, 139, 156 
Mustard, 219 
Sulphur in, 226 

Naphthalene, 272, 305 
Nascent state, 134 

Chlorine, 139, 140 

Hydrogen, 409 

Oxygen, 133, 134- 140, 164, 409 
Natural gas, 39, iii, 273 

B.t.u., 274 
Nature of gases, 56 
Negative electricity, 490 

Electrode, 209. See Cathode 

Photography, 468, 469 
Neon, III, 179 



526 



INDEX 



Neutralization, 143, 144, 204, 205 
And salts, 144 
Equation, 144, 205 
Ionic, 204, 205 
Ionic equation, 205 
Problems, 147 
Water in, 204, 205 
Neutral reaction, 143 
Newton's metal, 357 
Nichrome, 474 
Nickel, 479 

Alloys, 433, 474 
Catalyst, 302 
Coin, 433, 479 
Plating, 479 
- Steel, 406, 479 
Test, 479 
Nickelic salts, 479 
Nickelous salts, 479 
Niter, 372 

Pots, 236 
Niton, 487, 488 
Nitrates, 162 
And nitrites, 165 
Cellulose, 296 
Decomposition, 162, 163 
Oxides from, 167 
Test, 164 
Nitric acid, 159-170 
And copper, 163 
And metals, 163 
Aqua regia, 139 
Arc process, 168, 169 
Boiling point, 161 
Chemical conduct, 161 
Commercial, 160 
Duriron, 322 
Exercises, 170 
Formation, 159 
From air, 167 
From ammonia, 169 
From nitrogen oxides, 167 
Fuming, 167 



Manufacture, 160, 167-169 
Norway, 159 
Oxygen from, 161 
Preparation, 159 
Problems, 170 
Properties, 160 
Strong acid, 216 
Test, 164, 165 
Uses, 162 

Valence formula, 198 
Nitric oxide, 166 
And oxygen, 166 
By catalysis, 169 
Into nitric acid, 170 
Mole, 176 

Sulphuric acid, 234, 235 
Test, 166 

Volume relations, 174 
Nitrides, 104 
Nitrification, 163 
Nitrites, 165 

And nitrates, 165 
Nitrogen, 102-105 
And argon, iii 
And life, 104 
Atomic weight, 184 
Atoms in molecule, 175 

Boiling point, in, 112 

Chemical conduct, 103 

Dioxide, 166, 167 

Family, 333 

Forms ammonia, 151 

From ammonia, 151 

In air, 107 

Inert element, 104 

Name, 104 

Occurrence, 102 

Oxides, 104, 161, 163-169, 234 

Preparation, 102 

Properties, 103 

Test, 104, 148 

Tetroxide, 167 

Uses, 104 



INDEX 



527 



Nitrogen, weight of liter, 103, 493 
Nitrojrlyccrin, 302, 3ig 
Nitro-hydrochloric acid, 140 
Nit rose acid, 236 
Nitrosyl-sulphuric acid, 234 
Nitrous acid, 165 

Oxide, 157, 165, 166 
Noble metal, 140, 472 
Nodules, plant, 105 
Non-electrolytes, 205 

Molecular weight, 214 
Non-electrolytic solutions, 213 
Non-metals, 329, 330 

Aluminium, 420 

And anhydrides, 231 

And ions, 329 

Negative elements, 409 

Typical, 334 
Normal conditions, 55 

Gas volume, 54 

Salts, 231, 255 
Nucleus, atom, 490 
Nutrients, 307 
Nutrition, 307, 314 

Ocean, elements in, 8 

Water, 59 
Oil, cocoanut, 302 

Cottonseed, 301, 302 

Fats, 300, 301 

Fuel, 266 

Gas, 278 

Hydrogenation, 48, 302 

Lubricating, 270 

Olive, 301 
Oleic acid, 300 
Olein, 300, 301, 302 
Oleomargarine, 302 
Olive oil, 301 
Onions, 219 
Onyx, 317,377 
Ooze, 378 
Opal, 317 



Open hearth furnace, 401, 402 
Lining, 442 
Process, 401-404 
Charge, 403 
Orange mineral, 459 
Ore, 391 
Organic acids, 299, 300, 301 

Chemistry, 25, 198, 289 
Organic matter, 372 
Fertilizer, 105 
Oxidation, 60 

Sewage, 60 

Water, 59 
Orpiment, 354, 355 
Orthophosphates, 350 
Orthophosphoric acid, 347, 350 
Orthorhombic sulphur, 223 
Orthosilicic acid, 319, 321 
Osmium, 478 
Oxalic acid, 35, 256, 299 
Oxidation, 16, 17, 286, 409, 410, 454 

And ions, 410 

And oxides, 16 

And reduction, 46 

And valence, 409, 410 

Broad use, 409, 410, 454 

Hydrogen, 44 

In body, 20 

Iron chloride, 411 

Iron compounds, 408-413 

Nascent state, 134 

Of compounds, 17 

Organic matter, 60 

Ozone, 22 

Rapid, 17 

Slow, 17, 18 

Sulphuric acid, 239 

Sulphurous acid, 231 

Tin salts, 454 

Tissue, 309 
Oxides, 17 

And water, 68 

Common, 17 



528 



INDEX 



Oxides, names, 17 
Oxidizing agent, 16, 408 

Hydrogen peroxide, 84 

Nitric acid, 161 

Potassium dichromate, 475 

Potassium permanganate, 477 
Oxidizing flame, 285, 286 
Oxy-acetylene burner, 283 

Flame, 47, 48, 282, 283 

Outfit, 283 

Torch, 283 
Oxy acid, 145 
Oxygen, 12-23 

Acetylene flame, 282, 283 

Acids, 140 

Administering, 21 

And body, 20 

And digestion, 309 

And iron, 15 

And life, 20 

And mercuric oxide, 19 

And molecular weight, 174 

And nitrous oxide, 165 

And ozone, 22 

And sulphur, 15 

Atomic weight, 173, 184 

Atoms in molecule, 175 

Boiling point, 112 

Breathing, 21 

Breathing apparatus, 21, 22 

By electrolysis, 21 1 

Calculation of weight, 123 

Chemical change, 91 

Chemical conduct, 15, 16 

Compounds, 13, 15 

Cycle, 32 

Discovery, 12, 19 

Distribution, 12 

Equivalent weight, 185 

Exercises, 23 

Family, 333 

Formula, 97 

From chlorine water, 131 



From nitric acid, 161 

In air, 107 

In water, 77-82 

Manufacture, 20 

Mole, 176 

Molecular weight, 1 73 

Name, 19 

Nascent, 133, 134, 140, 164, 409 

Oxidizing agent, 16 

Plant, 13 

Plants, 31 

Preparation, 12, 13 

Properties, 14 

Removing from steel, 403 

Standard weight, 188 

Storing, 21 

Test, 16 

Uncombined atoms, 134 

Uses, 20 

Weight of liter, 14, 50, 56, 67, 493 
Oxy-hydrogen flame, 47, 48, 317 
Ozone, 22 

And oxygen, 22 

And water, 61 

Bleaching, 22 

Paint, 460 

Black, 25, 252 

Blackening, 460 

Green, 354 

Red, 459 

White, 388, 445, 460 

Yellow, 475 
Palladium, 478 
Palmitic acid, 300 
Palmitin, 300, 301 
Paper, 296-297 

Beater, 296 

Filter, 295 

ISIaking, 232, 296 

Parchment, 296 
Paraffin, 270 

Base, 270 



INDEX 



529 



PaiatViii, scries, 272 

Wax, 272 
Para-formal(lch)(lc-, 304 
Parchment paper, 296 
Paris green, 299, 355 
Parkes process, 457, 464, 465 
Particles, alpha, 485, 487, 491 
Beta, 486, 489 
In solution, 91 
Pearl ash, 373 
Pencils, lead, 246 
Pentad, 193, 195 
Pentahydrate, 97 
Pentane, 272 
Pentavalent clement, 193 
Percentage composition, 99 
And formula, 99, 100 
Problems, loi, 141 
Periodic classification, 330-336, 490 
Halogens, 343 
Law, 334 
Table, 331, 353 
Permanent hardness, 385 
Permanganate ions, 477 
Permutit, 386 
Petit, 185 
Petrified wood, 317 
Petroleum, 39, 267-271 
Agitators, 269 
Coke, 271 
Cracking, 268 
Distillates, 268, 271 
Industry, 267 
Look boxes, 271 
Properties, 267 
Refining, 268-271 
Sources, 267 
Stills, 269 
Well, 268 
Pewter, 454 
Phenol, 305 
Phlogiston, 18 
Phosphates, 346, 347, 35° 



Acid, 350 
And life, 350, 351 
Calcium, 350-352 
Dicalcium, 352 
Normal, 350 
Rock, 351 
Silver, 350 
Sodium, 350 
Test, 350 
Tricalcium, 352 
Phosphoric acid, 347, 349, 352 
Anhydride, 350 
Ions, 350 
Test, 350 
Phosphorus, 346-354 

And air, 103 

And life, 350 

Burning, 15, 281, 347, 348 

Cycle, 351 

Dangerous, 348 

Exercises, 358 

Fertilizer, 351 

Formula, 179, 348 

In food, 351 

In iron, 395 

In steel, 399 

Manufacture, 346, 347 

Matches, 15, 348, 349 

Ordinary, 347 

Pentoxide, 80, 103, 349 

Poisonous, 348 

Problems, 358 

Red, 348 

Sulphide, 349 

Variable formula, 179, 348 

White, 347 

With air, 107 

Yellow, 348 
Photography, 241, 341, 343. 4^8, 469 
Film, 2q6 
Flash light, 440 
Radium, 484 
Photomicrographs, 397, 406 



530 



INDEX 



Phylloxera, 218 
Physical change, 65 

Properties, 2 
Pickles, 142 
Picromerite, 372 
Pig iron, 395 
Pigment, 460, 462, 476 
Pintsch gas, 278 
Pitchblende, 480, 482 
Placer mining, 470 
Plant, hydrogen, 39 

Ice-making, 154 

Oxygen, 13 

Sulphuric acid, 235 
Plants, carbon dioxide, 31, no 

Food, 31, 105 

Leguminous, 105 

Sunlight, 31 
Plaster of Paris, 384 
Platinum, 236, 407, 478 

Alloys, 478 

Arsenide, 478 

Black, 478 

Catalyst, 45, 169, 233 

Family, 333 

Foil, 478 

Melting, 47 

Spongy, 478 

Substitute, 407, 478, 479 
Platinite, 407, 478, 479 
Plumbago, 246 
Plumbous plumbate, 459 
Poison gas, 131 

Hydrocyanic acid, 371 
Polonium, 489 
Porcelain, 423 

Lined vessels, 370 
Portland cement, 384 
Positive nucleus, 490 

Electrode, 209 

Photography, 469 
Potash, 373 

Caustic, 373, 374 



Prussiate of, 412 
Potassium, 371-374 

Acid fluoride, 337 

Acid tartrate, 374 

Aluminium silicate, 422 

And life, 374 

And water, 40 

Antimonyl tartrate, 356 

Atom in molecule, 1 79 

Bichromate, 475 

Bromide, 340, 341 

Carbonate, 373, 374 

Chlorate, 13, 14, 71, 97, 99, 117, 
120, 123, 207, 373 

Chloride, 14, 372, 373 

Chromate, 474 

Cobaltinitrite, 480 

Cyanide, 374 

Bichromate, 475 

Equivalent weight, 186 

Ferricyanide, 412, 413 

Ferrocyanide, 412, 413 

Fertilizer, 374, 375 

Fluoride, 338 

Gold cyanide, 472 

Hydroxide, 373 

Iodide, 342, 343 

Manganate, 477 

Nitrate, 104, 372 

Nitrite, 165, 372 

Permanganate, 231, 477 

Sulphate, 374 

Sulphocyanate, 413 

Tartrate, 299, 366 

Test, 372 
Pottery, 424 

Powder, baking, 30, 157, 350, 365, 
366, 374, 421 

Bleaching, 133 

Smokeless, 296 
Precautions, equation writing, 117 
Precipitate, 140 
Precipitation, 140 



INDEX 



531 



Pressure and Rases, 29, 30 
Atmospheric, 52 
Cooker, 67 
Corrected, 67 
Normal, 55 
Standard, 55 
Vapor, 65, 494 
Priestley, 12, 18 
Print, blue, 412 

Photographic, 468 
Problems, acids, 147 
Air, 114 

Aluminium, 424 
Ammonia, 157 

Atomic weights, 190, 191, 228, 243 
Balancing equations, 126 
Bases, 147 
Boyle's law, 54, 58 
Calcium compounds, 389 
Calories, food, 315 
Carbon, 258, 259 

Carbon dioxide, 38, 259 

Charles' law, 52, 58 

Chlorine, 141 

Composition, 11 

Copper, 437 

Equations, 147, 158 

Equivalent weights, 190 

Food, 315 

From equations, 127 

Fuels, 288 

Gas volumes, 58 

Gold and silver, 473 

Halogens, 344 

Hydrogen, 49, 58 

Hydrogen sulphide, 228 

Iron, 414 

Lead, 462 

Magnesium, 450 

Mercury, 451 

Metric system, 11 

Mole, 181 

Molecular formula, 181 



Molecular weight, loi 

Neutralization, 147 

Nitric acid, 170 

Oxygen, 23, 58 

Percentage composition, loi, 141 

Phosphorus, 358 

Potassium, 375 

Radium, 492 

Review, 217, 336 

Silicon, 328 

Simplest formula, loi, 141, 181, 

243, 259, 328 
Sodium, 375 
Sulphur, 228 
Sulphuric acid, 242 
Tin, 462 

Vapor density, 181 
Volume from equations, 127 
Volumetric, 158, 181, 228, 243, 

259 

Water, 85 

Weight from equations, 127 
Process, regenerative, 402 
Producer gas, 39, 274 
Propane, 272 
Properties, i 

Chemical, 2 

Compounds, 6 

Physical, 2 
Protein, 102 

Food, 308, 309, 311-313 

Function, 307 

Quantity needed, 311 
Prussian blue, 413 
Prussic acid, 371 
Ptyalin, 295 
Puddling, 396 
Pulmotor, 21, 34 
Pulp, wood, 296 
Purifier, gas, 275, 277 
Purple of Cassius, 472 
Putty, 379 
Pyrene, i35> 3^5 



532 



INDEX 



Pyrcx glass, 324 
Pyridine, 298 
Pyrites, 219, 391, 411 
Pyroligneous acid, 298 
Pyrolusite, 476 
Pyrosulphatcs, 241 
Pyrosulphuric acid, 241 
Pyrrhotite, 391 

Quadrivalent elements, 193 
Quartation, 471 
Quartz, 316, 318, 322 

Fused, 236, 317 
Quartzite, 318 
Quicklime, 379 
Quicksilver, 446 
Quinquivalent elements, 193 

Radiation, 485 
Radical, 143, 193 

Ammonium, 155 

And ions, 202 

Antimonj'l, 356 

Hydroxyl, 143 

Ions, 215 

Table, 194 

Table, ions, 214 

Valence, 193 

Valence rules, 196, 197 
Radioactivity, 483-487 
Radio-lead, 488 
Radium, 482-491 

And electrons, 490 

And uranium, 488 

Atom, 487 

Bromide, 482 

Carbonate, 483 

Chloride, 483 

Cost, 489 

Decomposing, 486 

Discover^', 482 

Disintegration products, 4: 

Emanation, 487, 489 



Flame test, 483 

General properties, 483 

Half period, 487 

Ionizes air, 484 

Isolation, 483 

Luminous mixtures, 489 

Photography, 484 

Series, 487 

Sulphate, 483 

Uses, 489 
Rain, 59, 65, 107 

Water, 59 
Ramsay, no, in 
Rayleigh, no 
Rays, 485 

Gamma, 485 
Reaction, 9, 115 

Acid, 142 

Alkaline, 143 

And equations, 125 

Basic, 143 

Ionic, 206, 207 

Neutral, 143 

Reversible, 152, 168 

Velocity, 152 
Reading equations, 119 
Realgar, 354, 355 
Red fire, 388 

Glass, 324 

Lead, 459 
Reducing agent, 34, 46, 409 

Aluminium, 417, 418 

Carbon monoxide, 34 

For gold, 470 

Hydrogen, 46 

Hydroquinone, 468 

Pyrogallic acid, 468 

Sulphurous acid, 231 
Reducing flame, 285, 286 
Reduction, 34, 46, 286 

And ions, 410 

And oxidation, 46 

And valence, 409, 410 



INDEX 



533 



Reduction, broad use, 409, 410, 454 
^ By carbon, 34, 252, 394 

Carbon monoxide, 34, 394 

Dextrose, 292 

Fehling's solution, 292 

Flame, 285, 286 

Hydrogen, 46 

Iron chloride, 411 

Iron compounds, 408-413 

Iron ore, 394 

Lead ore, 456, 457 

Mercury chlorides, 454 

Silver solution, 292 

Tin ore, 452 

Zinc ore, 443 
Refming petroleum, 268-271 
Refrigeration, 150 
Regenerative process, 402 
Relative humidity, 108 
Replacement, 42 

See Substitution 
Rescue apparatus, 21, 22 
Respiration, 20, 21 
Retorts, gas, 276 

Zinc, 443 
Reverberatory furnace, 396, 428 
Reversible equation, 152 
Reaction, 152, 168 
Rhombic sulphur, 223 
Richards, 187, 188, 488 
River water, 59 
Rock phosphate, 351 

Shell, 378 
Rocks, 59, 319 
Rose's metal, 357 
Rosin, 297 
Rouge, 410 
Royal water, 140 
Ruby, 419 
Rust, iron, 408 

Tin, 453 
Rusting, 15, 408 
Rutherford, 104 



Safety lamp, 273 

Sal ammoniac, 156 

Saleratus, 366 

Sal soda, 364 

Salt, common, 59, 362 

Dair>% 362 

Deliquescent, 75 

Glaze, 424 

Moist, 75, 362 

Standard, 362 

Table, 362 

Water, 59 
Saltpeter, 370, 371, 372 

Chile, 341, 342, 370, 371 
Salts, 142, 145, 204 

Abnormal behavior, 213 

Acid, 231, 240, 255, 365 

And ionization, 206 

And litmus, 142 

And valence, 197 

Basic, 454 

Composition, 143 

Dissociation, 202-216 

Electrolytes, 206 

Epsom, 240, 441 

Exercises, 146 

Formation, 139, 144, 145, 156, 207 

Formulas, 197 

Glauber's, 240, 369 

Hydrolysis, 365 

Ionic definition, 204 

Ionization, 202 

Naming, 145, 146 

Normal, 231, 255 

Properties, 143 

Rochelle, 434 

Smelling, 157 

Stassfurt, 372 
Sand, 316, 318 

Paper, 318 

See Silica 

See Silicon dioxide 

Uses, 318, 323 



534 



INDEX 



Sandstone, 318 
Saponification, 303 
Sapphire, 419 
Saturated solution, 70 
Scandium, 335 
Scrubber, 237, 276 
Seaweed, 341, 342 
Selenite, 384 
Selenium, 324 
Series, displacement, 435 

Electrochemical, 436 

Electromotive, 437 

Periodic, 332 
Serpentine, 319 
Shells, 378 
Shoe-blacking, 250 
Shot, 354, 459 
Sicily, sulphur, 218, 219 
Siderite, 391 
Silica, 316-318 

And alkalies, 318 

Etching, 339 

Fused, 317 

Lining, 399 
Silicates, 319-321, 324 

Decomposition, 319 

Etching, 338-339 

Fusible, 392 

Of soda, 320 

Slag, 392, 393, 394 

Sodium, 320 
Silicic acid, 319, 321, 323 

Colloidal, 321 

Meta-, 319, 321 

Ortho-, 319, 321 
Silicic anhydride, 321 
Silicides, 322 
Silicon, 316, 322 

And sodium hydroxide, 41, 322 

Carbide, 252, 322 

Electro-, 318 

Ferro-, 322 

In iron, 395, 396 



In steel making, 403 

Test, 323 

Tetrafluoride, 318, 323, 338, 339 
Silicon dioxide, 316-318, 321 

See Silica 
Silk, weighted, 455 
Silver, 464-468 

Alloys, 466 

Amalgamation, 464 

Ammonia chloride, 468 

Ammonium ion, 466 

Atomic weight, 185 

Bromide, 341, 468 

Chloride, 140, 468 

Cleaning, 466 

Coins, 466 

Complex ions, 466 

Cyanogen ion, 466 

German, 433, 479 

Halogen compounds, 241, 468 

In copper ore, 431 

In lead ore, 457 

Iodide, 343, 468 

Ion, 466 

Ionic test, 207 

Metallurgy, 464 

Nitrate, 466, 467 

Oxidized, 465 

Parkes process, 464, 465 

Phosphate, 350 

Photography, 241, 468, 469 

Plating, 467 

Properties, 465 

Quick-, 446 

Refining, 434, 465 

Separation from gold, 465, 471 

Sodium cyanide, 466, 467 

Specific heat, 185 

Sterling, 466 

Sulphate, 466 

Sulphide, 226, 464, 465 

Tarnishing, 226, 465, 466 

Test, 468 



INDEX 



535 



Silverware, tarnished, 226, 466 
Simplest formula, 99, 100, 177, 178 
And molecular formula, 178 
Problems, loi, 141 
Siphon, 2Q 
Sizing, 297 

Slag, 347. 392, 303' 394 
Aluminium oxide, 418, 419 
Copper, 429 
Thomas, 401 
Slaking lime, 380 
Slate, 319 
Sleet, 107 
Small calorie, 261 
Smalt, 480 
Smelting, 392 
Copper, 428 
Iron, 392 
Lead, 456 
See Metallurgy 
Smithsonite, 442 
Smoke, 27, 263 

Consumer, 263 
Smokeless powder, 296 
Snow, 59, 65, 107 
Crystals, 63, 64 
Soap, 301, 303, 320 
Cleansing, 303 
Hard water, 385 
Kettle, 303 
Manufacture, 303 
Soft, 373 
Soda, 365 
Ash, 363 
Baking, 299, 365 
Calcined, 364 
Caustic, 366 
Cooking, 3c, 365 
Sal, 364 
Silicates, 320 
Washing, 30, 364 
Water, 29, 69 
Sodium, 360-371 



Acetate, 300 

Acid carbonate, 363, 365 

Acid sulphite, 232 

And chlorine, 132 

And water, 40, 41, 361, 362 

Atom in molecule, 1 79 

Bicarbonate, 30, 32, 255, 365, 374 

Carbonate, 30, 255, 318, 363-365. 

369 
Carbonate, hydrolysis, 364 
Chloride, 129, 362, 363, 372, 490 
Chlorine salts, 146 
Cyanide, 371 
Bichromate, 475 
Equivalent weight, 186 
Family, 332 
Glass, 324 

Gold cyanide, 471, 472 
Hydrogen and, 40, 41, 361, 362 
Hydroxide, 13, 41, 129, 130, 210, 

211, 303. 360, 366-369 
Hypochlorite, 134 
H>'posulphite, 241, 468 
lodate, 341 
Ions, 202, 490 
Lactate, 299 

Manganate, 477 

Manufacture, 360 

Nitrate, 105, 159, 341, 37o, 372 

Nitrite, 103, 165 

Oleate, 303 

Palmitate, 303 

Peroxide, 13, 361, 37i 

Phosphates, 350 

Plumbite, 460 

Properties, 361 

Silicate, 320, 324 

Silver cyanide, 466, 467 

Stannate, 455 

Stearate, 303 

Sulphate, 240, 363, 364, 369 

Sulphide, 364 

Sulphite, 134, 230, 232, 342 



:)6' 



INDEX 



Sodium, test, 361 
Tetraborate, 369 
Thiosulphate, 72, 73, 241, 468 
Tungstate, 480 
Uranate, 480 
Soft coal, 18, 248, 250, 261 
Steel, 398, 405, 406 
Water, 385 
Solder, 370, 454, 459 
Solubility, and temperature, 70 
Curve, 7i> 72 
Limited, 70 
Mutual, 70 
See Solution 
Table, 71 
Soluble glass, 320 
Solute, 69 
Solution, 68-77 

And electric current, 205 
And pressure, 69 
Aqueous, 69 

Chemical behavior, 206-20S 
Colloidal, 76, 77 
Concentrated, 69 
Conductors, 205 
Crystallization, 71, 72 
Dilute, 69 

Electrolytes, 205, 213 
Electrolytic, 204, 205 
Freezing point, 212 
• Gases, 69 
Ions in, 206, 213 
Liquids, 69 
Molecules in, 213 
Nature, 75-77 
Non-electrolytes, 205, 213 
Particles in, 76, 77, 91 
Saturated, 70 
Solids, 70-75 
Supersaturated, 72, 73 
True, 76 
Two classes, 201 
What ions in, 214 



Solvay process, 363 
Solvent, 68, 69 
Sour milk, 293, 299 
Speculum metal, 454 
Spelter, 443 
Sperrylite, 478 
Sphalerite, 218, 442 
Spiegel iron, 396, 399 
Spinthariscope, 485, 489, 491 
Spontaneous combustion, 18 
Sprinkler head, 357 
Stalactites, 255, 377 
Stalagmites, 255, 377 
Stamp mill, 470 
Standard condition, 54, 55 
Stannic acids, 453, 455 

Chloride, 454, 455 

Compounds, 454, 455 

Hydroxide, 455 

Oxide, 325, 452, 453 
Stannous chloride, 452, 454 

Compounds, 454, 455 

Sulphate, 452 
Starch, 261, 293-295 

Alcohol from, 298 

And dextrin, 295 

And dextrose, 294 

And iodine, 294 

In baking powder, 374 

Plants, 31 

Solution, 75 

Suspension, 76 
. Test, 294, 343 
Stassfurt salts, 339^ 372, 439 
Steam, 64 

And metals, 41 
Stearic acid, 300, 301 
Stearin, 300, 301 
Steel, 398-407 

Alloys, 407 

Aluminium in, 417 

And monel metal, 479 

Bessemer, 398-401 



INDEX 



537 



Steel, brittle, 406 

Chromium, 404, 407 

Composition, 405 

Crucible, 404, 405 

Electric process, 405 

Hard, 404, 405, 406 

Hardness, 406 

Heat treatment, 406 

High speed, 407 

Manganese, 407 

Manufacture, 3Q8-405 

Mild, 405 

Molybdenum, 407 

Nickel, 406, 479 

Open hearth, 35, 401-404 

Properties, 405-407 

Soft, 398, 405, 406 

Special, 406 

Structural, 405 

Tempering, 406 

Tool, 405 

Tungsten, 407 

Vanadium, 407 

Wool, 15 
Sterling silver, 466 
Stibine, 356 
Stoneware, 424 
Storage battery, 459, 460 
Stove, 34, 35, 263-265 

Blast furnace, 393 

Fire in, 34, 35, 263 265 

Polish, 246 
Strontium nitrate, 388 

Salts, 388 

Test, 388 
Structural formulas, 198 
' Stucco, 384 
Sublimate, 156 
Sublimation, 156 

Ammonium chloride, 156 

Iodine, 342 
Substances, i 

And chemical change, 16 



Burning, 18, 19 

Chemical, 4 
Substitution, 42 

And valence, 196 

Copper oxide, 46 

Metal and acid, 42 
Sucrose, 289 
Suffix, acid, 146 

-ate, 146 

-ic, 141, 145, 195 

-ide, 145 

-ite, 145 

-ous, 141, 145, 195 

Salt, 146 
Sugar, 289-293 

Beet, 289, 290 

Cane, 289-291 

Charcoal, 290 

Evaporation, 67, 290, 291 

Fermentation, 298 

Fruit, 292 

Granulated, 291 

Grape, 292 

Manufacture, 290 

Milk, 292 

Raw, 290 

Reducing, 292 

Refined, 291 
Sulphates, 240 

Acid, 240 

Ionic test, 208 

Insoluble, 240, 241 

Normal, 240 

Pyro-, 241 

Soluble, 240 

Test, 208, 241 

Thio-, 241, 468 
Sulphides, 218, 222, 225 

H^'drogen, 224 

Iron, 391 
Sulphite, 232 

Acid, 231, 232 

Ndrmal, 231, 232 



538 



INDEX 



Sulphur,' 2 18-224 
Allotropic, 224 
American industry, 220 
Amorphous, 223 
And oxygen, 15 
Brunstone, 219 
Candle, 232 
Chemical conduct, 222 
Crystals, 223 
Deposits, 219 
Dioxide, 219, 229, 230, 232 
Flowers, 219 

From calcium sulphate, 218 
Heated, 222 
Industry, 219 
In gunpowder, 373 
In iron, 395 
In steel, 399 
Louisiana, 219 
Mining, 219 
Modifications, 222 

Molecules, 222 

Monatomic, 222 

Monochloride, 218, 221, 222 

Monoclinic, 223 

Occurrence, 218 

Orthorhombic, 223 

Oxidation, 15-17, 222 

Oxides, 17, 229-234, 237 

Plastic, 223 

Properties, 221 

Pure, 220 

Purification, 219 

Rhombic, 223 

Roll, 219 

Springs, 224 

Texas, 219 

Trioxide, 233, 237 

Uses, 218 

Variable formula, 179 

Well, 219, 220 
Sulphuretted hydrogen, 224, 225 
Sulphuric acid, 234-241 * 



And copper, 229, 239 

And iron, 239, 396 

And metals, 39, 40, 239 

And water, 238, 239 

Anhydride, 233 

Chamber process, 234 

Contact process, 237 

Electrolysis, 41, 211, 212 

Equation, 121, 122 

Fire extinguisher, 32, 33 

Formula, 99, 100 

Ionic test, 208 

Ions, 211, 212, 216, 240 

Manufacture, 234-238 

Nordhausen, 241 

Oxidation, 239 

Plant, 235 

Problems, 242 

Properties, 238 

Pyro-, 241 

Specific gravity, 236 

Test, 208, 241 

Use carefully, 238 

Uses, 240 
Sulphurous acid, 230, 231 

Anhydride, 231 
Superheater, 275 
Superphosphate, 352 
Supersaturation, 72, 73 
Suspension, 76, 77 
Sylvite, 372 
Symbols, 8 

Atomic weights, 97 
Exercises, 100 
Formulas, 97 
Ions, 203 
Meaning, 96, 97 
Table, 7, Back cover 
Synthesis, 79 

Ammonia, 151- 153 
Water, 79-82 

Table, atomic weights, Back cover 



INDEX 



539 



Table, earth's crust, 7 
Elements, 7 
Human body, S 
Ions, 214 
Metals, 330 
Ocean, 8 

Periodic, 331, 333, 335 
Solubility, 71 
Symbols, 7, Back cover 
Valence, 194, 195 
Weight of liter, 493 
Talc, 319 
Tallow, 301 

Tapping blast furnace, 394 
Tar, 276, 277 

Products, 305 
Tartar, 299 

Cream of, 299, 366, 374 
Emetic, 356 
Tartaric acid, 299 
Tartrates, 299 
Tellurium, 335 

Temperature and vapor pressure, 66 
Body, 27, 109 
Climate, 65 
Normal, 54 
Solubility, 70 
Standard, 54 
Tempering steel, 406 
Temporary hardness, 385 
Terracotta, 424 
Test, 16 

Acetic acid, 300 

Aluminium, 420 

Ammonium compounds, 156 

Antimony, 356 

Arsenic, 355 

Barium, 388 

Bead, 370 

Bismuth, 358 

Cadmium, 446 

Calcium, 386 

Carbon, 250 



Carbon dioxide, 27, 30, 253, 382 

Carbon monoxide, 257 

Chloride,. 1 40 

Chromium, 475 

Cobalt, 480 

Combined nitrogen, 148 

Copper, 433 

Dextrose, 292 

Ethyl alcohol, 300 

Ferric compounds, 412, 413 

Ferrous compounds, 412, 413 

Flame, 362, 372, 386, 388 

Glucose, 292, 434 

Gold, 472 

Hydrochloric acid, 140 

Hydrogen, 46 

Hydrogen chloride, 138 

Hydrogen sulphide, 226 

Ionic, 207, 208, 413 

Magnesium, 442 

Manganese, 477 

Mercury, 448, 449 

Moisture in air, 108 

Nickel, 479 

Nitrate, 164 

Nitric acid, 164, 165 

Nitrite, 165 

Oxygen, 16 

Potassium, 372 

Radium, 483 

Silicon, 323 

Silver, 468 

Sodium, 361 

Starch, 294 

Strontium, 388 

Sulphate, 208, 241 

Sulphuric acid, 241 

Tin, 454 

Zinc, 446 
Tetrad, 193, 195 
Tetravalent element, 193 
Texas sulphur, 219 
I Theory, 87 



540 



INDEX 



Theory, atomic, 89 

Disintegration of radium, 487 
Electrolytic dissociation, 201, 206 
Gases, 57, 90 
Ionization, 201, 206 
Kinetic, 57, 90 
Kinetic-molecular, 57, 90 
Molecular, 57, 90, 172 
Phlogiston, 18 
Thermal equation, 261, 262 
Thermit, 418, 419 
Thermo-chemical equation, 262 
Thermometer, 493 
Absolute, 51 
Centigrade, 51, 493 
High boiling, 104 
Scales, 51 
Thiosulphate, 241 

Photography, 468 
Thomas-Gilchrist process, 401 
Thorium, 480 
Meso-, 489 
Oxide, 286 
Radioactive, 489 
Tiles, 424 
Tin, 452-455 

Alloys, 356, 357, 433, 454 
And silk, 455 
Basic salt, 454 
Block, 62, 63, 452 
Crystals, 454 
Dioxide, 452, 455 
Disease, 453 
Family, 332 
Foil, 454 
Hydrolysis, 454 
Hydroxide, 455 
Ions, 454 
Metallurgy, 452 
Mordants, 455 
Ox>^muriate, 455 
Plate, 453 
Properties, 452 



Salt, 454 

Stannic compounds, 454, 455 

Stannous compounds, 454, 455 

Test, 454 

Uses, 453 

Valence, 454 
Toluene, 305 
Toning, 469 
Travertine, 377 
Triad, 193, 195 
Tribasic acid, 350 
Tripoli powder, 317 
Trivalent element, 193 
Tungsten, 407, 480 

Steel, 407 
TurnbuU's blue, 412 
Turpentine, 132 
Tuyeres, 392 
Type metal, 356, 459 

Ultra microscope, 91, 491 
Univalent element, 193 
Upward displacement, 149 
Uraninite, 480 
Uranium, 480 

And radium, 487, 488 

Atomic weight, 488 

Vacuum vessel, 67 
Valence, 192-199 

And atomic weight, 198 

And combination, 195 

And ions, 215-410 

And oxidation, 409, 410 

And reduction, 409, 410 

Defined, 193 

Determination, 198 

Displacement, 196 

Equivalent weights, T98 

Exercises, 199 

From atomic weights, 198 

Groups by, 333, 334 

Importance, 199 



INDEX 



S4I 



Valence, interpretation, 195, 196 
Learning, 336 
Of ion, 215 
Radicals, 193 
Representation, 193, 197 
Rules, 195, 197 
Salts, 197 
Substitution, 195 
Tables, 194, 195 
Terms, 193 
Variable, 195 

Writing formulas, 196, 197 
Vanadium, 404, 407 

Steel, 404, 407 
Vapor, 65 

Water, 65-67, 179 
Vapor density, 173, 174 

And atomic weights, 187 

And molecular weight, 174 

And oxygen, 173, 174 

Carbon dioxide, 1 73 

Method, 173 

Molecular formula, 178 
Vapor pressure, 65, 494 

And mercur}', 66 

And temperature, 66 

Application, 67 

At boiling point, 67 

At 100° C, 66, 67 

Deliquescence, 75 

Efflorescence, 74 

Experiments, 65, 66 

Maximum, 67 

Table, 494 

Water, 65 
Varnish, 298 
Vaseline, 270, 272 
Velocity and pressure, 152 

And catalyst, 153 
Hastening, 153 
Reaction, 152 
Vermilion, 449 
Vinegar, 142, 299 



Vitamins, 314 
Vitriol, blue, 240, 434 

Green, 240, 411 

White, 240, 445 
Volume, gram molecular, 176, 177 

Molar, 176 

Mole, 176 
Volumetric composition, 79, 81, 138, 
153, 179, 180 

Ecjuation, 179, 180 

Problems, 127, 181 

Wall board, 320 
Washing soda, 30, 385 
Water, 59-84 

Ammonia, 148, 150 

Analysis, 61 

And alcohol, 70 

And chlorine, 61 

And copper oxide, 46 

And ether, 70 

And heat, 68 

And hydrogen, 44 

And ions, 211, 364 

And metals, 40 

And oxides, 68 

And ozone, 61 

And sodium, 40, 361, 362 

And steam, 64 

.And sulphuric acid, 238, 239 

Bacteria in, 61 

Beverage, 63 

Boiled, 61 

Boiling point, 64 

Bromine, 341 

Chemical conduct, 68 

Chemical treatment, 61 

Chlorine, 77, 78, 13^ 

Composition, 41, 77-8-3 

Condenser, 62, 63 

Crystallization, 73, 74 

Decomposition, 13, 68 

Distillation, 62 



542 



INDEX 



Water, distilled, 62, 63 
Drinking, 60, 61 
Electrolysis, 78, 211 
Exercises, 84 
Expansion, 63 
Filtering, 60 
Foods, 59 
Formula, 198 
Freezing point, 63 
From ions, 205 
Gas, 35, 39, 274, 27s, 278 
Gases from, 13 
Glass, 320, 324 

Gravimetric composition, 79, 80 
Hard, 385, 386, 441 
Hardness, 385, 386, 441 
Household, 61 
Hydrogen in, 77, 81 
Hydrogen sulphide, 224 
Impure, 59 
In body, 59, 308 
In food, 309 
Ions, 205, 211, 212, 364 

Keeping, 61 

Lime, 381, 382 

Mineral, 69, 439 

Natural, 59, 69 

Need in body, 313 

Neutralization, 204, 205 

New York, 60, 61 

Occurrence, 59 

Ocean, 59 

Oxygen in, 77-82 

Ozone, 23 

Problems, 85 

Properties, 63 

Purification, 23, 59, 60, 61, 62, 434 

Qualitative composition, 77-79 

Quantitative composition, 79-81 

Rain, 59 

River, 59 

Royal, 140 

Salt, 59 



Sea, corrosive, 442 
Soda, 29, 69 
Sodium peroxide, 13 
Soft, 385, 386 
Softening, 385, 386 
Solvent power, 68 
Spraying, 60 
Stored, 60 
Synthesis, 79-82 
Three states, 64 
Underground, 69 
Vapor, 63, 64, 107-109, 179 
Vapor pressure, 65-67, 74, 75, 494 
Volumetric composition, 79, 81, 179 
Wax, paraffin, 270 
Weathering, 319 
Weight of liter, 55, 493 
Acetylene, 493 
Air, 493 

Ammonia, 150, 493 
And molecular weights, 172, 493 
Carbon dioxide, 29, 253, 493 
Carbon monoxide, 33, 493 
Chlorine, 131, 493 
Ethylene, 493 
Hydrogen, 43, 493 
Hydrogen chloride, 137, 493 
Hydrogen sulphide, 493 
Methane, 493 
Nitric oxide, 493 
Nitrogen, 103, 493 
Nitrous oxide, 493 
Oxygen, 14, 50, 56, 67, 493 
Sulphur dioxide, 253, 493 
Welding, 47, 283, 395 
By thermit, 418 
Oxy-acetylene, 283 
Wrought iron, 397 
Welsbach light, 286 

Mantle, 480 
WTietstone, 318, 323 
Whey, 293 
White lead, 460 



INDEX 



543 



White lead, blackening, 226 

Manufacture, 461 
WTiite vitriol, 445 
Whitewash, 382 
Whiting, 379 
Willemite, 442 
Wintergreen, 300 
Wood alcohol, 250, 267 
Wood and paper, 232 

Ashes, 371, 373, 374 

B.t.u., 267 

Burning, 265 

Cellulose, 295 

Paper, 296, 297 

Petrified, 317 

Pulp, 218 

Silicified, 317 
Wood's metal, 357 
World War, 131 
Writing equations, 115-119 
Wrought iron, 396 -398 

Xenon, in 
X-rays, 486 
Spectrum, 490 

Yeast, 295 

And alcohol, 298 

And bread, 295 
Yellowstone Park, 319 

Zero, absolute, 51 
Group, 487 



Zinc, 442-446, 471 
Alloys, 433, 444 
Amalgamated, 447 
And sulphuric acid, 42 
Atom in molecule, 179 
Blende, 218, 442 
Carbonate, 442 
Chloride, 445 
Complex compound, 445 
Dust, 443 

Electric cell, 436, 437 
Electrolytic, 443 
Equivalent weight, 186, 189 
Family, 332 
Flame test, 446 
Granulated, 444 
Hydroxide, 445 
Ions, 436, 444 

Metallurgy, 443 

Ores, 442 

Oxide, 442, 444> 445 > 460 

Poisonous salts, 445 

Properties, 443 

Sihcates, 442 

Sulphate, 240, 445 

Sulphide, 218, 225, 442, 445, 486 

Test, 446 

Uses, 444 

White, 445 
Zincates, 444, 445 
Zincite, 442 

Zones, blast furnace, 394 
Zymase, 298 



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